One of the interesting fact that I found in using DPM backing up SQL.
One database had a recovery model FULL couldn’t synchronize the log files content to DPM.
In the SQL server side, after going through the event viewer, realised that the event ID 5, Active Server Pages. This error occurred at the same time as the backup.
Resolution : re-register the asp.dll from an elevated command prompt.
Thanks to Robert Hedblom for his sharing.
Hope this helps you as it helps me.
keynotes : SQL synchronization sync error, event view 5, Active Server Pages, regsvr32 asp.dll