Unexpected Server reboots with Stop Error 0x0000007f - Event ID 1076

Hi there - wonder if anyone can shed any light on an intermittent issue we have.

We have several Windows 2003 servers that have unexpectantly rebooted over the past few months reporting

System Failure: Stop Error
Reason Code: 0x805000f
Bugcheck String : 0x0000007f (0x00000008, 0xf772ffe0, 0x00000000, 0x00000000)

All these servers have Symantec Endpoint Protection 11.0.4000.2295
Symantec Backup Exec 11d

We also use Altiris and all the normal agents are on the servers. Also Volume Shadow copy is being used.

Any opinions/views are most welcome.

Thanks in advance