Okay, so the error is when creating a config backup...
...but it's still not clear which version we are talking about here.
Don't worry about what you did 3 months ago, and don't worry about restoring backups.
Which version are you using now when you see the problem during backup creation?
By the way, the configuration is all stored in normal files (not in the registry) so you can back it up manually if you need to. The way to do that is explained here.