Could not load file or assembly error 

Your ASP.NET 2.0 site may receive an error similar to below when uploading a new ascx component to an existing site.

Could not load file or assembly 'App_Web_********, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified.

This is a known bug with ASP.NET 2.0 and the only known workaround is to force a recompile of the entire site. This can be done by switching the debug mode in the web.config and reloading the site before switching it back.