Could not load file or assembly 'AjaxControlToolkit' or one of its dependencies. The parameter is incorrect. (Exception from HRESULT: 0x80070057 (E_INVALIDARG)) [Updated]

The title of this post is common error for .net developers. Sometimes, when you try to run your project, you may get this error

Could not load file or assembly 'AjaxControlToolkit' or one of its dependencies. The parameter is incorrect. (Exception from HRESULT: 0x80070057 (E_INVALIDARG))

There is a number of blog posts available on different websites. I have clubbed them here for quick view. Follow them step by step, that may resolve the issue.

Remove all files from following path: 

Windows 7 x86 / XP
C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files.

Windows Vista
C:\Users\<UserName>\AppData\Local\Temp\Temporary ASP.NET Files

 Windows 7 x64
C:\WINDOWS\Microsoft.NET\Framework x64\v2.0.50727\Temporary ASP.NET Files.

Close your solution and re-open the same.

Your issue will be resolved :)

[Update on 21 Feb 2013]
If you are .net framework 4.0 or higher try removing temp files from below path:

Windows 7 x86
C:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files

Windows 7 x64
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files
One more alternative solution
If your application is configured to run on port:80 in IIS 7 or IIS 7.5 (this can be checked from the properties window of your Visual Studio Solution). Set it to run on auto selected port number.

This is not the actual solution, but this alternative solution may save your day.

By AlpesH Shah