Dave,
If the server is crashing, this should have nothing to do with encryption. I have some suggestions/questions for you:
1. What happens if you try a job to tape without encryption?
2. What happens if you try a job to disk with/without encryption?
3. Does this happen every single time you run a job with encryption or every once in a while?
4. Are you noticing the crash occurring at the same point every time? Please refer to the job log to see when it occurs.
5. Is this a duplicate job from disk to tape, or a standard job going directly to tape?
6. If Backup Exec crashes, what service is causing it...you should be able to find this out in Windows Event Viewer.
Thanks.