Could not load file or assembly 'Microsoft.SharePoint.ApplicationPages'
Recently I received following error on SharePoint: Could not load file or assembly 'Microsoft.SharePoint.ApplicationPages, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c' or one of its dependencies. Access is denied. … In the error, we can see that obviously we do not have permission, but who is trying to access the DLL? It is not the Application Pool account, but the Anonymous IIS account. Simple fix, check to see what account is running in Directory Security, give read permission to that user for the _app_bin folder, and recycle the application pool. Should be fixed.