Time Machine Error - Help!

Hello everyone. I am having a problem with backing up my time machine in Lion and get the following error message: "The backup was not performed because an error occurred while copying files to the backup disk. The problem may be temporary. Try again later to back up. If the problem persists, use Disk Utility to repair your backup disk."

Here is the context and history. I recently installed Mavericks on my Mac Mini (late 2009), which was causing all sorts of problems and constant computer crashes. About a week later I used TM to restore to the previous OS version and backup (Lion) before the problems began, and the computer is now working normally as before, except for TM. Initially I thought it was a problem with the drive, so I tried a TM back-up on my second back-up disk but got the same above error message. Thinking it had something to do still with the disk or older back-ups there saved, I erased one of the disks (using disk utility), performed disk repair, tried another TM back-up but continue to get the same error message. Any suggestions of next steps to try? I am not great with code or computer speak, so would greatly appreciate easy instructions if possible.

One last thing to note, this problem only began after doing the TM restore mentioned above. TM was still working normally even with Mavericks, so intuitively I am guessing something went wrnong during the restore, but everything seems to be working fine except with TM. I have done disk repairs also on the Mac HD and no errors were found. Please help!

Cheers!