Recently upgraded to SQL 2005 on our admin server and, since then, backups don't appear to be going too well.
We back up C:, D: and the System State to tape.
What's happening is that C: is being backed up but then the tape is ejected without giving the chance for D: to start or the System State.
I can guarantee that the tape cannot be full because the C: drive hasn't even got 10GB of data on it and the entire system can usually fit on a tape.
Both drives can also back up individually when I perform a test backup.
Something I thought of was that maybe the SIMS database would be in a locked state and therefore not allow a backup so last night I stopped the SQL Server service and the SQL Server Agent service but this didn't make any difference.
*EDIT* - sorry, running Windows Server 2003 R2 if that's any help