debugger enfeebled by "The activation context being deactivated is not the..."

[GeoRanger]

I'm trying to debug a native C++ application which uses MFC as a DLL. This in VS 2008 on a Windows 7 machine. The code I'm debugging has some bad pointers and out-of-bounds array indices.

My perception is that until about one or two months ago, bugs like this would make the program crash with a GP Fault and the debugger would nicely take you to the bad instruction or at least to a problem which was ultimately caused by the bad code. In contrast, when this happens now, I'm instead getting the red herring "0xC015000F: The activation context being deactivated is not the most recently activated one." The call stack that I get with this error never has even the slightest thing to do with the code where the problem is really located, nor do the call stacks of any of the other threads in the application.

The code I'm debugging is not using .NET and I don't give a rip about SxS assemblies or manifest files. I checked the related post here http://www.codeguru.com/forum/showthread.php?t=511101 but I can't tell that it's related.

Since it seems to have started happening a month or two ago, I also looked through my recent Windows updates and VS updates, but nothing jumped out at me. (That's not to mean that didn't overlook something.)

Does anybody know what might be causing this? I just want the debugger to work the way it used to. It's taking me roughly an order of magnitude (base 10) longer to debug because of this.

Thanks for ideas