Hello,
The answers to your questions are:
Yes, backup job finished successfully, just it took 2,5 hours to put it on DAT72 and consumed time frame for other jobs.
I make backup of four Windows 2003 Servers including server in question. The problem appears only with this server.
In a job I backup disk C and Shadow Components only. The only major application is MS SQL Server. The databases of MS SQL located on disk D. This server is remote to the server with a tape, so I use agents.
I also have another server with MS SQL there and I have no problem with it.