I have had a problem un-installing CFP, I used the ‘remove programmes’ in the control panel as usual. (I was testing different firewalls for suitability) : 
Anyhow, the uninstall seemed ok but, I later found it wasn’t. After testing a couple more I decided that comodo was for me, and tried to re-install it. I kept getting a banner saying comodo already installed, do you wish to uninstall, I clicked yes, simply because I had no comodo icon on the desktop, and could find no files ANYWHERE!! The uninstall did not happen. I’m not a pc whizz but I tried all I know and I can’t shift it, basically I have cfp somewhere on my system but can’t find any file holding it, so I can uninstall and start over… HELP!!! :o
Greetings!
What version of CFP are you trying to uninstall?
Cheers,
Ragwing
As far as I know the latest: 3.0.15.277 on XP Home
Have you tried to to a complete uninstall?
It should remove all files (and registry entries), and make you able to install CFP 3.
Cheers,
Ragwing