Backup Exec scheduled job causes crash

I have 2 clients with a similar problem. Both have newly installed Backup Exec 9.1. One is NT 4.0 Server the other is Win2003 SBS. Both systems crash during the execution of a scheduled backup job. They use different new backup drives ( one Sony DAT the other Seagate Travan) The crash may well be similar to a crowbarred power supply in symptom. There is no event log entry to associate to in either. The after the fact Event entry indicates a time the system crashed which can be manually correlated with the Backup Exec job detail log. Does anyone know exactly what will cure this?