Pidgin: No protocols listed

I've installed Portable Gaim on several pcs on my classroom but on three of them there are no protocols listed when the students try to add an account. We've downloaded, unzipped and used the Portable Gaim several times on those machines but it still doesn't works.

Obviously this problem is related to win setup (all pcs are cloned from an original) but I couldn't find the real reason.
Any idea? Thanks in advance...