We've had a few instances where a backup job (long term to tape) fails. When we try to resume the backups by selecting "Resume tape backups...", it causes every data source in the protection group to backup to individual tapes rather than consolidating the backups onto one-tape (as it normally does on the scheduled jobs.)
We found this powershell script posted by from Mike Jacquet that works great to overcome the multiple tape issue! http://social.technet.microsoft.com/Forums/en-US/dpmtapebackuprecovery/thread/4fafbcb0-ac2c-4867-8434-31f1f5e532e0/#7b40ef6e-d8bd-4a24-aecd-5f1605e80225
After modifying it to work with DPM 2012 by adjusting line 25 to DPM 2012's SQL instance, $instance = '.\msdpm2012', we were able to run it to re-trigger one of our failed weekly tape backup. Hopefully this post will be a bit easier to find - but credit still goes to Mike and Wilson, I'm only the messenger. We did notice that you need to be sure and inactivate any alerts that are still active and it takes a minute or two to see the jobs kick off.