I too had problems when up-grading from 2.6 - 2.7 (pro). I uninstalled pro and searched for all limewire files. I then trashed all limewire files from the free version (except my shared files) leaving the pro-installer on the decktop. I then reinstalled limewire pro with no problems.

That's a problem I had in 2002. Since then, I have up-graded smoothly many times . Good Luck