After much grief, I figured it out.
When uninstalling AMD drivers and moving to an earlier version, the included uninstaller does not, in fact (even after a reboot!), uninstall all drivers, devices, and software properly, leading to corrupted drivers, malfunctioning software, and endless BSOD loops upon restart (aaarghhh!!!) The BSOD loops, of course, will also cause Windows filesystem corruption after awhile, leading to even more driver errors, loss of internet access, data corruption, etc., and each time you run the Windows 'repair' or 'filecheck' utilities, you pretty much guaranteed to break something new.
In this case, among other issues, my OpenCL driver was not functioning correctly, even though the installer(s) (both Catalyst and SDK) swore up and down it loaded just fine, and repairing it multiple times all ensured me I had a functional install each time...
Guiminer, GPU Caps Viewer, and poclbm all gave me that unhelpful crash message, but the newest GPU-Z was more helpful, telling me I had a bad OpenCL driver (just before crashing, of course). Of course, GPU-Z confusingly claimed it was an INTEL OpenCL driver that was broken (wrong), despite the fact that I have no integrated graphics, and an ATI video card...but oh well.
If anyone else wants to downgrade from 13.1, run the AMD uninstall utility, restart in safe mode, run the uninstall a second time (only partially worked the first time), delete all folders beginning with ATI or AMD in the Program files and program files (x64) directories. Then restart again in safe mode, and clean up regis0rty keys, and C:\Windows\assembly files, and uninstall your video cards via device manager. Restart into normal mode, and you should be able to install an older version of Catalyst. If you get a BSOD loop, something's only partially uninstalled. Except that didn't work for me either, so I ended up installing Catalyst software suite 12.8, then upgrading everything except the Control Center to 12.10 (the 12.10 control center still refuses to start for me...) I'm probably missing a step or two, but you get the general idea >.< Chances are your video card manufacturer only has the 13.1 drivers, so youll have to get older ones from the AMD website. And no, according to AMD, there is no way to install *just* the OpenCL drivers. You either have to go through the Catalyst suite, or the SDK installer. Don't use Driver Sweeper to uninstall anything, it will only cause pain. You should probably avoid CCleaner too.
If this sounds like a huge pain, it definitely is. In other words, Don't upgrade AMD Catalyst to 13.1. It seems to be extremely buggy, and downgrading is a huge pain, and certainly not guaranteed to work well either. I read plenty of forum threads where the only solution to an attempted downgrade was reformatting and reinstalling Windows
My computer's definitely buggier than what it was 2 days ago, but at least I'm (mostly) back to a working video card driver. And GUIMiner/poclbm run once again.
The most annoying part of all this is that it took me almost all day just to get a HELPFUL error message to figure out exactly what was happening, rather than random stack overflow warnings and APPCRASH hashes.
Frustrated, and going to sleep,
Zithras
