Can't solve the "An exception of type 'System.Data.SqlClient.SqlException' occurred in System.Data.dll but was not handled in user code"

Question

I have a form in which you can enter your email and then receives instructions on resetting the password. It has a textbox (txtEmail), a Submit button (btnResetPassword) and a lblMessage.

My C# code looks like this:

protected void btnResetPassword_Click(object sender, EventArgs e)
{
    string CS = ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;

    using (SqlConnection con = new SqlConnection(CS))
    {
        SqlCommand cmd = new SqlCommand("spResetPassword", con);
        cmd.CommandType = CommandType.StoredProcedure;

        SqlParameter paramEmail = new SqlParameter("@Email", txtEmail.Text);
        cmd.Parameters.Add(paramEmail);

        con.Open();

        SqlDataReader rdr = cmd.ExecuteReader();

        while (rdr.Read())
        {
            if (Convert.ToBoolean(rdr["ReturnCode"]))
            {
                SendPasswordResetEmail(rdr["Email"].ToString(), rdr["UniqueId"].ToString());
                lblMessage.Text = "An email with instructions to reset your password is sent to your registered email";
            }
            else
            {
                lblMessage.ForeColor = System.Drawing.Color.Red;
                lblMessage.Text = "Username not found!";
            }
        }
    }
} 

I then have a method SendPasswordResetEmail(string email, string ID) which works fine (SMTP).

The stored procedure is:

CREATE PROC Spresetpassword @Email NVARCHAR(100) 
AS 
BEGIN 
    DECLARE @UserId INT 

    SELECT @UserId = id 
    FROM dbo.turiststbl 
    WHERE email = @Email 

    IF (@UserId IS NOT NULL) 
    BEGIN 
        --If username exists 
        DECLARE @GUID UNIQUEIDENTIFIER 

        SET @GUID = Newid() 

        INSERT INTO tblresetpasswordrequests (id, userid, resetrequestdatetime)
        VALUES (@GUID, @UserId, Getdate()) 

        SELECT 
            1 AS ReturnCode, 
            @GUID AS UniqueId, 
            @Email AS Email 
    END 
    ELSE 
    BEGIN 
        --If username does not exist 
        SELECT 
            0 AS ReturnCode, 
            NULL AS UniqueId, 
            NULL AS Email 
    END
END

When I enter my email, I get the following error:

See Screenshot Here

What can I do?
Edit: Database files are not local, they are on a remote server

Answer 1

The problem origins from connection string inside web.config file:

<connectionStrings> 
    <add name="DefaultConnection" connectionString="Data Source=(LocalDb)\MSSQLLocalDB;
    AttachDbFilename=|DataDirector‌​y|\aspnet-Vizito-201‌​70305102044.mdf;
    Init‌​ial Catalog=aspnet-Vizito-20170305102044;
    Integrated Security=True" providerName="System.Data.SqlClient" />
</connectionStrings>

Here you're attempting to use LocalDb instance by mentioning AttachDbFilename parameter on connecting string attribute, and it shouldn't use Initial Catalog parameter on the same string.

Hence, by removing Initial Catalog part, the connection string should be like this:

<connectionStrings> 
    <add name="DefaultConnection" connectionString="Data Source=(LocalDb)\MSSQLLocalDB;
    AttachDbFilename=|DataDirector‌​y|\aspnet-Vizito-201‌​70305102044.mdf;
    Integrated Security=True" providerName="System.Data.SqlClient" />
</connectionStrings>

Additionally, if the database file placed outside of App_Data directory inside the project, you may require full file path to refer its location as this:

<connectionStrings> 
    <add name="DefaultConnection" connectionString="Data Source=(LocalDb)\MSSQLLocalDB;
    AttachDbFilename=C:\Users\Hp-Pc\Desktop\VizitoSiteMaster\Vizito\App_Data\aspn‌​et-Vizito-2017030510‌​2044.mdf;
    Integrated Security=True" providerName="System.Data.SqlClient" />
</connectionStrings>

Update:

According to OP explaining that the DB takes place on remote server instance, the connection string should use Initial Catalog like this:

<connectionStrings> 
    <add name="DefaultConnection" connectionString="Data Source=[server address];
    Init‌​ial Catalog=aspnet-Vizito-20170305102044; User Id=[user ID]; Password=[password]; 
    Integrated Security=SSPI" providerName="System.Data.SqlClient" />
</connectionStrings>

NB: Replace [server address] with remote server IP address (with port if exists), [user ID] & [password] with user credentials used on the remote server.

References:

SQL Server Connection String

Cannot attach the file *.mdf as database

An attempt to attach an auto-named database for file ....database1.mdf failed