You're probably getting your iTunes library all in order to make it ready for a nice new operating system. If so, you'll want to pick up the latest version of Dupin, the iTunes Duplicates Manager.
This latest version fixes a few rare bugs: a case-sensitivity issue with files located on an NAS that prevented Purging, errant detection of iTunes Match being enabled when it actually isn't, a Selection Window flickering problem, no longer wheezes if you happen to move the iTunes Media folder while Dupin is running, and a few other way-out-there situations are accomodated.
You can get version 2.8.2 by using Dupin's "Check for Update..." command in its app menu, or download it directly from here.
This is a free update for registered users of v2.5 and later. Otherwise, Dupin is $15.