I can’t say I’ve seen this particular error, but I’m wondering if that might be stored in the .suo file associated with your solution. The .suo is where VS tracks which files you had open previously, so maybe it tracks failed ones as well. You might try renaming or deleting that file and then reloading the solution to see if the error goes away. Unfortunately, those files aren’t entirely human-readable, so if that proves to be the location, it may not be trivial to determine which file was at fault.