If you have a weird backup error on the symantec backup server exec server you may want to turn on debug logging on the backup exec agent for the server in question to help you diagnose the problem.
To do this first stop the "Backup Exec Remote Agent for Windows Systems" service on the server with the problem.
Edit the properties of the service and int he start parameters enter -debug
Next you need to enable debugging in the registry:
HKLM\Software\Symantec\Backup Exec for Windows\Backup Exec\Engine\Logging
Change the DWORD CreateDebugLog to "1" to enable debug logging:
Next start the "Backup Exec Remote Agent for Windows Systems" service again.
The logs will be located in this folder:
C:\Program Files\Symantec\Backup Exec\RAWS\logs
Start the backup and review the client log file for additional information as to what caused it to error out.