Why Does My ASP.NET Web Forms Application Throw a 'System.MissingMethodException'?

Troubleshooting "System.MissingMethodException: Method not found" in ASP.NET Web Forms

The Issue:

An ASP.NET Web Forms application, previously functional, now produces a "System.MissingMethodException: Method not found" error when calling the DoThis method within a generic handler.

Background:

• The DoThis method resides in the same class as the generic handler.
• The generic handler's implementation:

<code class="language-csharp">public class MyHandler : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
      // Now throws System.MissingMethodException: Method not found.
      this.DoThis(); 
    }

    public void DoThis() { ... }
}</code>

Solution:

This exception typically arises from a version conflict between the DLL containing DoThis and the application's referenced DLL. Here's how to fix it:

1. Clean Up Compiled Files: Remove all files from the ~/App_Code/bin and ~/bin/ directories. This ensures no outdated compiled code interferes.

2. Rebuild and Redeploy: Perform a clean rebuild of your solution and redeploy it to your server. This guarantees the deployment of the most up-to-date assembly versions.

3. Eliminate Duplicate Assemblies: Check for any duplicate or older assemblies residing in hidden folders, such as ~/bin/Debug or ~/bin/Release. Remove any unnecessary or outdated versions.

By following these steps, the "System.MissingMethodException: Method not found" error should be resolved, allowing your application to correctly call the DoThis method.

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