Backup of my tables didn't work, and instead of a meaningful error message telling me what's wrong, or even steps how to solve the problem, all I got was this:
After trying some stuff I noticed that the user doing the backup had insufficient rights to access some internal MySQL tables. So I started the backup again after loggin in with the "root" MySQL user and it instantly worked.
In a serious software project a misleading error message like the above would be considered as a bug.