Why is it that i get all the weird *** problems?

Anyway...

A customer has a tape driver
Travan 8 gig (Seagate)... And it likes to reboot the computer while it's backin up...
Than backup gets fugged....

Any ideas why it reboots? I turned off power mgt so that's not it, and all screensavers are off.....

Pls respond..
-Machine