Fixing ROM checksums/headers to work on the Super UFO Pro 8

I've got this annoying problem, where the Super UFO Pro 8 will refuse to load a ROM ("Bad file type") if the internal checksum is bad. I'd really, really like to run the "Controller Test Cassette" but no matter what I do with ucon64 I can't seem to get it to work, little help guys?

http://superfamicom.org/info/controller-test-cassette

 

Don't have a Super UFO to test, try this one Link.

 

I have this device and yea, it refuses to load a lot of roms. I still don't know what error exactly it is, but it's not as simple as the checksum. I *think* it fails to determine the file size or mapping in those "bad" roms (that load fine on any other flash cart).