Hi!
So, you just need to click with the right mouse button on the Assembly-CSharp and then click on the “Reload” option.
Hope to help with your problem!
Just simply close and reopen mono. That my solution whenever I get that error, if it’s still not ok just do it one more time
Old post but had to resolve the same issue, which I could not find an answer to.
To solve this issue:
- Close Unity
- Delete all .csproj files from project root folder.
- Run Unity, which will rebuild these files.