MSBuild threw error: "... task could not be instantiated from the assembly"

Question

EDIT: Never mind, it turns that out the task does not actually implement the Microsoft.Build.Framework.ITask interface. I had made the erroneous assumption that it did. D'oh!

I use Visual Studio 2015.

Relevant code:

string solutionFilePath = args.Single();

var fileLogger = new FileLogger { Verbosity = LoggerVerbosity.Detailed, Parameters = @"logfile=C:\MSBuildResults.txt" };
var projectCollection = new ProjectCollection {DefaultToolsVersion = "14.0"};
var buildParameters = new BuildParameters(projectCollection) { Loggers = new List<ILogger> { fileLogger } };

var globalProperties = new Dictionary<string, string> { { "Configuration", "Debug" }, { "Platform", "Any CPU" } };
var buildRequestData = new BuildRequestData(solutionFilePath,
                                            globalProperties,
                                            targetsToBuild: new[] { "Build" },
                                            toolsVersion: "14.0",
                                            hostServices: null);

BuildResult buildResult = BuildManager.DefaultBuildManager.Build(buildParameters, buildRequestData);

buildResult.OverallResult is BuildResultCode.Failure, with error messages like the following printed to my log file:

C:\Workspaces\SomeProject.csproj(67,5): error MSB4127: The "DummyTask" task could not be instantiated from the assembly "\networkDrive\Dummy.dll". Please verify the task assembly has been built using the same version of the Microsoft.Build.Framework assembly as the one installed on your computer and that your host application is not missing a binding redirect for Microsoft.Build.Framework. Unable to cast object of type 'DummyTask' to type 'Microsoft.Build.Framework.ITask'.

Following the advice here, I added the <bindingRedirect> tag in the .exe.config file of my program. The same error messages were thrown nonetheless.

Instead of using Microsoft.Build libraries, I decided to invoke MSBuild.exe using Process.Start() (which I know is not recommended):

var processStartInfo = new ProcessStartInfo(@"C:\Program Files (x86)\MSBuild\14.0\Bin\MSBuild.exe") 
{
      Arguments = $"{solutionFilePath} /t:Build",
      RedirectStandardOutput = false,
      UseShellExecute = true,
      CreateNoWindow = false
};
var process = Process.Start(processStartInfo);

process.WaitForExit();            
process.Close();

This time, the build was successful and the process ran to completion with exit code 0.

What did I do wrong when using Microsoft.Build libraries to build my solution? What should I do instead to ensure that the build succeeds when I use BuildManager?

Let me know if you need any more information to help me with my issue.