"Failed to write meta file" After upgrading project to Unity 4.5

I was making a game with Unity 4.1 and wanted to use Draw Call Minimizer, which obviously requires Unity 4.3 or higher, so I updated to the free version of 4.5.

Now, when I open the project I was working on I get these two errors that won't go away:

(Last sentence in both error messages means: "The system could not find the specified path")

Literally, every time I minimize and then maximize Unity they pop up.

This is weird because I did not move or change anything in the project. In fact, all I did was uninstall 4.1 and then install 4.5. That's all.

I'm still relatively new to Unity and making games in general so I was wondering if anyone can explain exactly what went wrong and what I can do to fix it.

Thank you very much for your time!