Would you like to try an older version of iTunes, to see whether that works?
Like I said, I'm using iTunes 7 & there are no probs with the latest stable LW or the Beta versions.
Maybe this is an issue with iTunes 9 - check out the links below.
Is The New iTunes 9, Limewire Resistant? - Yahoo! Answers Apple - Support - Discussions - Limewire Itunes Connection ... (though this one tells you to change the location of LW's download folder)
It can be a bit of a pain to revert to an older iTunes & preserve your library etc... depends whether you have heaps of files in your iTunes library. If you're interested in trying that, rather than losing your Pro LW then check out this link for info:
http://www.gnutellaforums.com/327806-post4.html