Not sure if this ever got resolved.
I had this problem.. . I have a grandfathered dvdfab account that should always have mobile..
but today... man I could not get the registration to stick in... just kept wanting me to register/purchase/enter key.. I was pissed I couldn't get this thing running the mobile options..
So, I read this forum and did the recommended FULL uninstall(including registry deletions, show-hidden file deletions, folder deletions.. and finally the reboot.
I had a lot of dvd fab files/folders/registry keys from several years of owning this I guess.. I think the software just got confused, and it needed a spring cleaning.
I'm on vista 32, and this just happened out of nowhere, ( or with the update )...
Anyways, it worked. First try after the reboot, I redownloaded, re-installed and voila.