Reimporting didn't work either
Viewing post in Weird error preventing my builds from running
Sorry bro, can't really help you that much. I can only give you a suggestion, although it's up to you if you want to.
- If you know StackOverflow or UnityForums, you can search or ask there. I recommend this before doing anything else.
- Try to reinvent the game to another game project, not the best solution.
I have game project before that was re-imported to another Unity Version (newer than back to older). The project too was corrupted.