.NET Assembly Hell
There are times when .NET tries one’s patience as a developer. A very common problem on a development machine is that ASP.NET suddenly begins to throw "Configuration Errors" without warning, saying that particular assemblies cannot be loaded. The assemblies concerned are fine; what is actually happening is that ASP.NET’s local cache of the assemblies (in a location something like C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322\Temporary ASP.NET Files\aftrs\798cb90a) are being locked by another process.
Usually that other process is the Indexing Service on your Windows machine. The solution is to turn that service off, or make it exclude the ASP.NET cache folders. See http://support.microsoft.com/default.aspx?scid=kb;en-us;329065.
