Macbook Pro HANGS - Can anyone help?

To whoever reads this, thank you in advance. My UbMBP 13 inch becomes completely non-functional from time to time - and won't work until I do a manual reboot by switching it off and turning it on by pressing the power button.

Could someone help me understand what may be wrong with my system? I've posted the data below.

Thank you.


ERROR REPORT

Wed Apr 7 20:20:39
panic(cpu 1 caller 0x2269e4): "thread_invoke: preemption_level -1, possible cause: unlocking an unlocked mutex or spinlock"@/SourceCache/xnu/xnu-1504.3.12/osfmk/kern/sched_prim.c:1471
Backtrace (CPU 1), Frame : Return Address (4 potential args on stack)
0x5899be18 : 0x21b449 (0x5ce420 0x5899be4c 0x2238a5 0x0)
0x5899be68 : 0x2269e4 (0x585e1c 0xffffffff 0x585db4 0x2262a8)
0x5899bee8 : 0x2270ea (0x813bb98 0x0 0x43dd7000 0x1)
0x5899bf58 : 0x227155 (0x22fa8f 0x863ea0 0x0 0x2a1596)
0x5899bf78 : 0x22fc29 (0x22fa8f 0x863ea0 0x0 0x0)
0x5899bfc8 : 0x29e6cc (0x863ea0 0x0 0x10 0x8b0b9e0)

BSD process name corresponding to current thread: kernel_task

Mac OS version:
10D573

Kernel version:
Darwin Kernel Version 10.3.0: Fri Feb 26 11:58:09; root:xnu-1504.3.12~1/RELEASE_I386
System model name: MacBookPro5,5

I'm definitely going to take it to an AASP. But was hoping someone could help me understand what's going wrong before that. Thank you to all of you for your helpful advice though. And If anyone does know what this is about, please do let me know.

Thank you

No - I haven't been able to figure out the case. Spoke to an Apple technician on the phone, he said to repair permissions, reset pram etc etc. The basic steps (don't quite remember all of them) That hasn't helped. I've tested my ram with Tech Tool Pro 5, it doesn't seem to indicate any problems with the ram sticks.

Jockye2 - I haven't been able to figure out what the problem is yet. If you manage to find the cause before I do, let me know.

Thank you to everyone who has taken the time out to suggest solutions.

Alright, I'll take it in to an AASP. Jockey2 - I'll let you know when they let me know what's wrong. But it may take a while because the AASP in my area works at their own pace. Thank you everyone for your help.

I'm not using any of these - neither VMware Fusion (Version 3.0.2 and 3.1), Parallels, or VirtualBox. I even changed my hard drive to rule out boot issues and the problem is still occurring. If anyone has any updates or solutions to this problem, please let us know.
Thanks.

Yes. This is a fresh install - installed from the 10.6 Macbook Pro discs. It seems to be more of a Mac hardware issue than a hard disk issue. The same issue is occurring with 2 different hard disks indicating the common factor may be the Macbook Pro instead of the hard disks. However if anyone has any more helpful information, I'd appreciate it. I will update when I receive any more information also. As always, thank you for your help.