system intermittently rebooting when processors loaded

We have a dual Opteron 250 (accelertech board) with 16Gb of infineon ram LSI Megaraid controller and SCSI raid array running SLES 9 trying to run abaqus. The SLES install is out of the box with just YOU patches installed. We can run a single job on 1 cpu basically indefinitely but when trying to run a second job the machine will intermittently reboot, does anyone have any idea's of where I should start looking to try and trace this problem ? This happens with both the 32bit version of abaqus (running fine on a Dell 2650 with Suse 8) and the beta 64bit versions. Any ideas gratefully received. Thanks Paul