Do you know what can cause this problem? I am not able to back up two files due to a strange error message: Invalid signature. Unfortunately, this error message is not documented in the knowledge base on the CB website.
It's best to open a support case with us by sending us the logs via the Tools | Diagnostic toolbar option. I prefer to avoid sending instructions on a fix for another customer that may not address your particular issue.
In one of the tickets the issue has been resolved without any input from our side and we didn't get any feedback in the other ticket. Still, I would suggest to synchronize the repository via tools > options > repository menu just in case.