I have a SQL 2005 SP 2 server running a maintenance plan that performs full backups every day at 22:00, diff backups every 4 hours and log backups every 30 minutes. The plan backs up all system & user databases (all user DBs are in Full recovery mode). The full & log backups all complete and verify without problem - i've confirmed this by doing some test restores. Every morning the diff backup throws an error from 2 databases stating that no full backup exists.
It's always the same two databases that have this error - all others are ok. If I manually run a full backup again the diff's will run fine until the next morning.
I'm fairly certain that the problem is down to a VSS backup that is run at midnight by the company that manage the servers using Bacula. In the SQL logs I can see that VSS is freezing/thawing the system DBs and these 2 databases only when Bacula runs.
Obviously I can just get the hosting Co to stop backing up the DBs within their job since they're picking up my SQL backup files anyway but I simply want to know why this is happening. What could be different about these 2 databases as every option i've checked is identical to the ones that complete fine. I have the same plan set-up on another server which runs with no problems.