Hey that worked! I did a registry cleanup (using the tool inside Advanced Uninstaller Pro, but I think any registry cleaner does about the same things) and it started working again!
I suspect that one of Microsoft's updates left some sort of errant registry entry regarding .Net's most recent updates. Doing a cleanup probably either removes or repairs it. Thanks for pointing me that way, Alex! I really needed this to be working on my laptop and now it is.