Some times it's not enough just to be the administrator, in this case you should run the set-up with the right-click-administrator.
Done.
If you set a point for system-restore before you installed the prog, you could go back and try a clean re-install.
Done.
When you tried it several times in vain, it's better to clean the caches and temp-files, maybe even delete the GOTD cookies.
Done, also every single file, that could have been created by that software and I know about :) was deleted.
And please never forget to unpack the downloaded zip-file to the desktop or any folder before running set-up.exe. Just running the file from within the archive, mostly fails.
I could be wrong, but if you use WinRAR, it unpacks the files into temporary data folder, that is placed in the same directory (almost) with desktop files. Anyway I moved the files into other partition and the result it still the same. I don't expect any official support and in fact it was said like that, but I think even in the case I backup my OS to 2010, it will be the same.
I wonder if people that have the same issue use the 32 or 64-bit version of the Windows.
Some times we just have to accept that our unique system doesn't like this or that.
About that, it depends on in what way the application gets the informations concerning the registration process and how that info is stored. If someone knows the fact, it would be nice to know as well, as it could help to get know what is wrong.