Microsoft claims it is a hardware error - RAM, MB or mismatched memeory modules. None of which should be affected by Perfect Disk upgrades.
But if you look at their detail info it could result from perfect disk trying to check more hard disk than exists. Still not a solution (other than a different optimizer, I've stayed with perfect disk 6 because all the latter ones were clunkier or had issues.)...
From MS
To determine an approximate cause, examine the parameters at the top of the STOP screen:
**STOP 0x0000007F (0x000000XX, 0x00000000, 0x00000000, 0x00000000)
UNEXPECTED_KERNEL_MODE_TRAP
The most important parameter is the first one (0x0000000X) which may have several different values. The cause of this trap can vary, depending on the value of this parameter. All traps that cause a STOP 0x7F can be found in any Intel x86 microprocessor reference manual as they are specific to the x86 platform. Here are some of the most common ones: Values Meaning ---------- -------------------- 0x00000000 Divide by Zero Error
0x00000004 Overflow
0x00000005 Bounds Check Fault
0x00000006 Invalid Opcode
0x00000008 Double Fault