There seem to be a couple of bugs here; the first is that we are unable to update the palringo login details for an existing account, and second, we are then unable to delete the non-functioning account if it is the first or only account in the list.
The first bug is apparent both in the OSX and iPhone versions of palringo, but the second is only in the OSX version. A work-around for it -- if you have an iPhone -- is to delete the rogue account from the iPhone app, which, of course, will also delete it in the OSX version.
What do mean you don't have an iPhone!