Sounds like you fellas may have some registry entries left over that are causing some "grief"
I would try this:
Uninstall PD7
Run Wise Registry Cleaner (A free program from www.wisecleaner.com/download.html )
Then install your purchased version of PD7 and try to run the patch.
You may have some "leftovers" in the registry from PD5 as well, uninstalling a program does not always get rid of all registry entries and the uninstall, install, uninstall, install again routine often attempted keeps leaving irrelevant registry "stuff" there. Then when you try to run a patch that finds this "crap" and "barfs"
Wise Registry Cleaner is a very good little utility and I use it every time I have to uninstall something (after the uninstall). It seems to find these "leftovers" and gets rid of them for me.
Good luck.