I’ve been hit by this lovely error a number of times over the past year when attempting to run unit tests in Visual Studio 2005. I always end up searching for the answer, encountering the fifty or so different “solutions” that fail horribly. So now I save it here.
The fix is to reset your environment in Visual Studio. You can do this by opening a Visual Studio Command Prompt (MS Visual Studio 2005 -> Visual Studio Tools from the start menu) and run the following command (PLEASE READ ON prior to running this! Important stuff comes later!):
This brings Visual Studio back to the primordial stage. Unfortunately, you lose all your settings. That includes all your tricky VS fonts and colors customizations. You won’t lose your Add-ins, however. So if you want to save and then reload all your UI customizations, you’d better save them first.