Not a computer guru but I'll offer this; I've only had a similar issue with Norton upgrades and RealFlight. It sounds like you've run the possibilities I would have run by going through the computer and the registry looking for orphan files after the un-install. From past experience, I'd say you have to do a reboot after all that and before attempting to re-install the program. The only other thing I do is to run a Norton Utility I have which will identify bad registry entries.

Have you tried calling the KnifeEdge guys?