Its hard to diagnose problems like this.  I have win7 and have upgraded and installed beta's as well.  I did have a problem a while back but not with carrara turns out something in the .net app system messed up and certain .net apps wouldn't run it was very frustrating.  Something underlying got corrupted and there was no way to 'fix' so I had to re-install.  I didn't know it was .net apps as there was no real message.  The author of a screensaver I use had a lightbulb moment when the software didn't run.  He sent me a 'hello world' app as a .net app and that pinpointed the problem.