PyQt Crash - Access violation writing location 0x00000000
===

I'm writing an application in PyQt on Windows XP that has multiple windows, dialogs, etc, and also uses OpenCV to display a video stream (processed into pixmaps via PyQt).  Upon launching the program and doing some preliminary communication with external serial devices, it displays all the windows and their components, including the video feed, and then (sometimes) throws this message:

Unhandled exception at 0x6700223f in pythonw.exe: 0xC0000005: Access violation writing location 0x00000000.

The first address changes but the second two (0xC0000005 and 0x00000000) are always the same...apparently it's a null pointer reference?

Here is the line that Visual Studio points me to (marked with a "*"), with some of the surrounding lines:

>6700227D  int         3  
6700227E  int         3  
6700227F  int         3  
67002280  mov         eax,dword ptr [ecx]  
67002282  or          edx,0FFFFFFFFh  
* 67002285  lock xadd   dword ptr [eax],edx  
67002289  jne         67002294  
6700228B  mov         eax,dword ptr [ecx]  
6700228D  push        eax  
6700228E  call        67056670  
67002293  pop         ecx  
67002294  ret  
67002295  int         3  
67002296  int         3  

I looked into this a bit and this site (http://www.riverbankcomputing.com/pipermail/pyqt/2011-August/030378.html) reported that this is a long-standing bug involving Qt and garbage collection, and put an alternative garbage collection class in my main thread, which had initially seemed to take care of this, but now I've been getting this issue fairly regularly.  

One other thing, I've been running this program on an older Pentium 4 running Windows XP, and have not encountered this issue once on that machine.  However, on this machine, a quad core i5, I'd say I get this crash 1/5 to 1/10 times I launch the program.

I'm pretty stumped here, I know very little about debugging C++ and the internals of Qt, and any help is greatly appreciated!  I'd be glad to provide any further information that may be useful in solving this problem.