Problem using DLL file in an ASPX page with .NET framework, cannot find file

Question

I'm still trying to learn the .NET framework so please excuse my ignorance.

I am trying to create an ASP.NET web application and trying to use a DLL file that will encrypt and decrypt a string that looks something like this (not with the encrypt function):

namespace MyLib
{
    public class Dencrypter
    {
        public string Decrypt(string input, string key)
        {
            // Create an array to hold the input sting
            byte[] arr = Convert.FromBase64String(input);

            // Create and initialize 
            TripleDESCryptoServiceProvider tripleDES = new TripleDESCryptoServiceProvider();
            tripleDES.Padding = PaddingMode.PKCS7;
            tripleDES.Mode = CipherMode.ECB;
            tripleDES.Key = UTF8Encoding.UTF8.GetBytes(key);

            // Create decryptor object
            ICryptoTransform trans = tripleDES.CreateDecryptor();

            // Decrypt and store in result array
            byte[] result = trans.TransformFinalBlock(arr, 0, arr.Length);
            tripleDES.Clear();

            return UTF8Encoding.UTF8.GetString(result);
        }
    }
}

I have a very simple ASPX web form pretty much with one button and a text box, whose code behind is simply something like this:

using MyLib;
namespace Proj5Assign8{
    public partial class _Default : Page
    {
        protected void DecryptClick(object sender, EventArgs e)
        {
            Dencrypter dencrypt = new Dencrypter();
            string key = "ahfkvmwbghxjfklt";
            string str = DencryptBox.Text;
            string result = dencrypt.Decrypt(str, key);
            DencryptLabel.Text = result;
        }
    }
}

I first compile MyLib into a DLL file and the add the project reference to my ASP.NET project, but when I try testing the web page in my browser I get a file not found error:

Could not load file or assembly 'System.Runtime, Version=4.2.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.

My DLL file works in a separate console application just fine, and my ASPX page works fine if I dont use MyLib. I've already tried this solution, and the one attached to the link with no luck.

Somebody said this problem can happen if the solution is not explicitly opened, but just the folder the solution is in, or you could explicitly open the file ending with .csproj but I had no luck with this.

Here is my web app project file:

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <Import Project="..\packages\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.2.0.1\build\net46\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.props" Condition="Exists('..\packages\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.2.0.1\build\net46\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.props')" />
  <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
  <PropertyGroup>
    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
    <ProductVersion>
    </ProductVersion>
    <SchemaVersion>2.0</SchemaVersion>
    <ProjectGuid>{E01C56D9-27E7-4A6B-A57F-A1119FB7817B}</ProjectGuid>
    <ProjectTypeGuids>{349c5851-65df-11da-9384-00065b846f21};{fae04ec0-301f-11d3-bf4b-00c04f79efbc}</ProjectTypeGuids>
    <OutputType>Library</OutputType>
    <AppDesignerFolder>Properties</AppDesignerFolder>
    <RootNamespace>Proj5Assign8</RootNamespace>
    <AssemblyName>Proj5Assign8</AssemblyName>
    <TargetFrameworkVersion>v4.7.2</TargetFrameworkVersion>
    <UseIISExpress>true</UseIISExpress>
    <Use64BitIISExpress />
    <IISExpressSSLPort>44340</IISExpressSSLPort>
    <IISExpressAnonymousAuthentication />
    <IISExpressWindowsAuthentication />
    <IISExpressUseClassicPipelineMode />
    <UseGlobalApplicationHostFile />
    <NuGetPackageImportStamp>
    </NuGetPackageImportStamp>
  </PropertyGroup>
  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
    <DebugSymbols>true</DebugSymbols>
    <DebugType>full</DebugType>
    <Optimize>false</Optimize>
    <OutputPath>bin\</OutputPath>
    <DefineConstants>DEBUG;TRACE</DefineConstants>
    <ErrorReport>prompt</ErrorReport>
    <WarningLevel>4</WarningLevel>
  </PropertyGroup>
  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
    <DebugSymbols>true</DebugSymbols>
    <DebugType>pdbonly</DebugType>
    <Optimize>true</Optimize>
    <OutputPath>bin\</OutputPath>
    <DefineConstants>TRACE</DefineConstants>
    <ErrorReport>prompt</ErrorReport>
    <WarningLevel>4</WarningLevel>
  </PropertyGroup>
  <ItemGroup>
    <Reference Include="Microsoft.CSharp" />
    <Reference Include="MyLib">
      <HintPath>..\..\DLLComp\MyLib\MyLib\bin\Debug\netcoreapp3.1\MyLib.dll</HintPath>
    </Reference>
    <Reference Include="System.ComponentModel.DataAnnotations" />
    <Reference Include="System" />
    <Reference Include="System.Data" />
    <Reference Include="System.Core" />
    <Reference Include="System.Data.DataSetExtensions" />
    <Reference Include="System.Web.Extensions" />
    <Reference Include="System.Xml.Linq" />
    <Reference Include="System.Drawing" />
    <Reference Include="System.Web" />
    <Reference Include="System.Xml" />
    <Reference Include="System.Configuration" />
    <Reference Include="System.Web.Services" />
    <Reference Include="System.EnterpriseServices" />
    <Reference Include="System.Web.DynamicData" />
    <Reference Include="System.Web.Entity" />
    <Reference Include="System.Web.ApplicationServices" />
    <Reference Include="Microsoft.Web.Infrastructure, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
      <Private>True</Private>
      <HintPath>..\packages\Microsoft.Web.Infrastructure.1.0.0.0\lib\net40\Microsoft.Web.Infrastructure.dll</HintPath>
    </Reference>
    <Reference Include="AspNet.ScriptManager.bootstrap">
      <HintPath>..\packages\AspNet.ScriptManager.bootstrap.3.4.1\lib\net45\AspNet.ScriptManager.bootstrap.dll</HintPath>
    </Reference>
    <Reference Include="AspNet.ScriptManager.jQuery">
      <HintPath>..\packages\AspNet.ScriptManager.jQuery.3.4.1\lib\net45\AspNet.ScriptManager.jQuery.dll</HintPath>
    </Reference>
    <Reference Include="Microsoft.ScriptManager.MSAjax">
      <HintPath>..\packages\Microsoft.AspNet.ScriptManager.MSAjax.5.0.0\lib\net45\Microsoft.ScriptManager.MSAjax.dll</HintPath>
    </Reference>
    <Reference Include="Microsoft.ScriptManager.WebForms">
      <HintPath>..\packages\Microsoft.AspNet.ScriptManager.WebForms.5.0.0\lib\net45\Microsoft.ScriptManager.WebForms.dll</HintPath>
    </Reference>
    <Reference Include="System.Web.Optimization, Version=1.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35">
      <HintPath>..\packages\Microsoft.AspNet.Web.Optimization.1.1.3\lib\net40\System.Web.Optimization.dll</HintPath>
    </Reference>
    <Reference Include="Newtonsoft.Json">
      <HintPath>..\packages\Newtonsoft.Json.12.0.2\lib\net45\Newtonsoft.Json.dll</HintPath>
    </Reference>
    <Reference Include="WebGrease">
      <Private>True</Private>
      <HintPath>..\packages\WebGrease.1.6.0\lib\WebGrease.dll</HintPath>
    </Reference>
    <Reference Include="Antlr3.Runtime">
      <Private>True</Private>
      <HintPath>..\packages\Antlr.3.5.0.2\lib\Antlr3.Runtime.dll</HintPath>
    </Reference>
    <Reference Include="Microsoft.AspNet.Web.Optimization.WebForms">
      <Private>True</Private>
      <HintPath>..\packages\Microsoft.AspNet.Web.Optimization.WebForms.1.1.3\lib\net45\Microsoft.AspNet.Web.Optimization.WebForms.dll</HintPath>
    </Reference>
    <Reference Include="Microsoft.AspNet.FriendlyUrls">
      <HintPath>..\packages\Microsoft.AspNet.FriendlyUrls.Core.1.0.2\lib\net45\Microsoft.AspNet.FriendlyUrls.dll</HintPath>
    </Reference>
  </ItemGroup>
  <ItemGroup>
    <Reference Include="Microsoft.CodeDom.Providers.DotNetCompilerPlatform">
      <HintPath>..\packages\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.2.0.1\lib\net45\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.dll</HintPath>
    </Reference>
  </ItemGroup>
  <ItemGroup>
    <Content Include="About.aspx" />
    <Content Include="Contact.aspx" />
    <Content Include="Content\bootstrap-theme.css" />
    <Content Include="Content\bootstrap-theme.min.css" />
    <Content Include="Content\bootstrap.css" />
    <Content Include="Content\bootstrap.min.css" />
    <Content Include="Content\Site.css" />
    <Content Include="Default.aspx" />
    <Content Include="favicon.ico" />
    <Content Include="fonts\glyphicons-halflings-regular.svg" />
    <Content Include="Global.asax" />
    <Content Include="fonts\glyphicons-halflings-regular.woff2" />
    <Content Include="fonts\glyphicons-halflings-regular.woff" />
    <Content Include="fonts\glyphicons-halflings-regular.ttf" />
    <Content Include="fonts\glyphicons-halflings-regular.eot" />
    <Content Include="Content\bootstrap.min.css.map" />
    <Content Include="Content\bootstrap.css.map" />
    <Content Include="Content\bootstrap-theme.min.css.map" />
    <Content Include="Content\bootstrap-theme.css.map" />
    <None Include="Scripts\jquery-3.4.1.intellisense.js" />
    <Content Include="Scripts\bootstrap.js" />
    <Content Include="Scripts\bootstrap.min.js" />
    <Content Include="Scripts\jquery-3.4.1.js" />
    <Content Include="Scripts\jquery-3.4.1.min.js" />
    <Content Include="Scripts\jquery-3.4.1.slim.js" />
    <Content Include="Scripts\jquery-3.4.1.slim.min.js" />
    <Content Include="Scripts\modernizr-2.8.3.js" />
    <Content Include="Scripts\WebForms\DetailsView.js" />
    <Content Include="Scripts\WebForms\Focus.js" />
    <Content Include="Scripts\WebForms\GridView.js" />
    <Content Include="Scripts\WebForms\Menu.js" />
    <Content Include="Scripts\WebForms\MenuStandards.js" />
    <Content Include="Scripts\WebForms\MSAjax\MicrosoftAjax.js" />
    <Content Include="Scripts\WebForms\MSAjax\MicrosoftAjaxApplicationServices.js" />
    <Content Include="Scripts\WebForms\MSAjax\MicrosoftAjaxComponentModel.js" />
    <Content Include="Scripts\WebForms\MSAjax\MicrosoftAjaxCore.js" />
    <Content Include="Scripts\WebForms\MSAjax\MicrosoftAjaxGlobalization.js" />
    <Content Include="Scripts\WebForms\MSAjax\MicrosoftAjaxHistory.js" />
    <Content Include="Scripts\WebForms\MSAjax\MicrosoftAjaxNetwork.js" />
    <Content Include="Scripts\WebForms\MSAjax\MicrosoftAjaxSerialization.js" />
    <Content Include="Scripts\WebForms\MSAjax\MicrosoftAjaxTimer.js" />
    <Content Include="Scripts\WebForms\MSAjax\MicrosoftAjaxWebForms.js" />
    <Content Include="Scripts\WebForms\MSAjax\MicrosoftAjaxWebServices.js" />
    <Content Include="Scripts\WebForms\SmartNav.js" />
    <Content Include="Scripts\WebForms\TreeView.js" />
    <Content Include="Scripts\WebForms\WebForms.js" />
    <Content Include="Scripts\WebForms\WebParts.js" />
    <Content Include="Scripts\WebForms\WebUIValidation.js" />
    <Content Include="Site.Master" />
    <Content Include="ViewSwitcher.ascx" />
    <Content Include="Web.config" />
    <Content Include="Bundle.config" />
    <Content Include="Site.Mobile.Master" />
  </ItemGroup>
  <ItemGroup>
    <Compile Include="App_Start\BundleConfig.cs" />
    <Compile Include="About.aspx.cs">
      <DependentUpon>About.aspx</DependentUpon>
      <SubType>ASPXCodeBehind</SubType>
    </Compile>
    <Compile Include="About.aspx.designer.cs">
      <DependentUpon>About.aspx</DependentUpon>
    </Compile>
    <Compile Include="App_Start\RouteConfig.cs" />
    <Compile Include="Contact.aspx.cs">
      <DependentUpon>Contact.aspx</DependentUpon>
      <SubType>ASPXCodeBehind</SubType>
    </Compile>
    <Compile Include="Contact.aspx.designer.cs">
      <DependentUpon>Contact.aspx</DependentUpon>
    </Compile>
    <Compile Include="Default.aspx.cs">
      <DependentUpon>Default.aspx</DependentUpon>
      <SubType>ASPXCodeBehind</SubType>
    </Compile>
    <Compile Include="Default.aspx.designer.cs">
      <DependentUpon>Default.aspx</DependentUpon>
    </Compile>
    <Compile Include="Global.asax.cs">
      <DependentUpon>Global.asax</DependentUpon>
    </Compile>
    <Compile Include="Properties\AssemblyInfo.cs" />
    <Compile Include="Site.Master.cs">
      <DependentUpon>Site.Master</DependentUpon>
      <SubType>ASPXCodeBehind</SubType>
    </Compile>
    <Compile Include="Site.Master.designer.cs">
      <DependentUpon>Site.Master</DependentUpon>
    </Compile>
    <Compile Include="Site.Mobile.Master.cs">
      <DependentUpon>Site.Mobile.Master</DependentUpon>
      <SubType>ASPXCodeBehind</SubType>
    </Compile>
    <Compile Include="Site.Mobile.Master.designer.cs">
      <DependentUpon>Site.Mobile.Master</DependentUpon>
    </Compile>
    <Compile Include="ViewSwitcher.ascx.cs">
      <DependentUpon>ViewSwitcher.ascx</DependentUpon>
      <SubType>ASPXCodeBehind</SubType>
    </Compile>
    <Compile Include="ViewSwitcher.ascx.designer.cs">
      <DependentUpon>ViewSwitcher.ascx</DependentUpon>
    </Compile>
  </ItemGroup>
  <ItemGroup>
    <Folder Include="App_Data\" />
  </ItemGroup>
  <ItemGroup>
    <None Include="packages.config" />
    <Content Include="Scripts\jquery-3.4.1.slim.min.map" />
    <Content Include="Scripts\jquery-3.4.1.min.map" />
    <None Include="Web.Debug.config">
      <DependentUpon>Web.config</DependentUpon>
    </None>
    <None Include="Web.Release.config">
      <DependentUpon>Web.config</DependentUpon>
    </None>
  </ItemGroup>
  <PropertyGroup>
    <VisualStudioVersion Condition="'$(VisualStudioVersion)' == ''">10.0</VisualStudioVersion>
    <VSToolsPath Condition="'$(VSToolsPath)' == ''">$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v$(VisualStudioVersion)</VSToolsPath>
  </PropertyGroup>
  <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
  <Import Project="$(VSToolsPath)\WebApplications\Microsoft.WebApplication.targets" Condition="'$(VSToolsPath)' != ''" />
  <Import Project="$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v10.0\WebApplications\Microsoft.WebApplication.targets" Condition="false" />
  <ProjectExtensions>
    <VisualStudio>
      <FlavorProperties GUID="{349c5851-65df-11da-9384-00065b846f21}">
        <WebProjectProperties>
          <UseIIS>True</UseIIS>
          <AutoAssignPort>True</AutoAssignPort>
          <DevelopmentServerPort>62633</DevelopmentServerPort>
          <DevelopmentServerVPath>/</DevelopmentServerVPath>
          <IISUrl>https://localhost:44340/</IISUrl>
          <NTLMAuthentication>False</NTLMAuthentication>
          <UseCustomServer>False</UseCustomServer>
          <CustomServerUrl>
          </CustomServerUrl>
          <SaveServerSettingsInUserFile>False</SaveServerSettingsInUserFile>
        </WebProjectProperties>
      </FlavorProperties>
    </VisualStudio>
  </ProjectExtensions>
  <Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild">
    <PropertyGroup>
      <ErrorText>This project references NuGet package(s) that are missing on this computer. Use NuGet Package Restore to download them.  For more information, see http://go.microsoft.com/fwlink/?LinkID=322105. The missing file is {0}.</ErrorText>
    </PropertyGroup>
    <Error Condition="!Exists('..\packages\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.2.0.1\build\net46\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.props')" Text="$([System.String]::Format('$(ErrorText)', '..\packages\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.2.0.1\build\net46\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.props'))" />
  </Target>
  <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
       Other similar extension points exist, see Microsoft.Common.targets.
  <Target Name="BeforeBuild">
  </Target>
  <Target Name="AfterBuild">
  </Target>
  -->
</Project>

and then MyLib .csproj file

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>
  </PropertyGroup>

</Project>