It's a pretty vague error... looking at the changes I made I can't figure out what could cause that. You say it worked on the last guiminer? One thing you could try is deleting your miners and creating new miners just to see if that does anything.

Another thing you could try is to run poclbm from the command line and see if that works correctly, in case there was an issue with the latest poclbm. If you look in the console when you start tup you can see the command to use, something like:

poclbm.exe kiv:pass@localhost:8332 --device=1 --platform=0 --verbose -r1