Recently I was configuring SharePoint Forms Based Authentication (FBA) to use a custom login screen, Active Directory Membership Provider, and my own Role Provider, when I received the following: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...