Hi Lois-
Generally speaking, the PCLZIP_ERR_BAD_FORMAT error means that the backup archive was somehow corrupt.
We might be able to determine what went wrong based on the archive log on your main site. Navigate to Total Upkeep > Tools > Logs and look for the log file with a name like archive-XXXXX.log
and the timestamp corresponding to when you took the backup.
We’re looking for the last few lines of that log, where you should see a message like Backup complete!
or else find some evidence of errors that happened during the backup process. If you can paste those log entries here, we can investigate further and get you all fixed.