My last tire rotation I encountered the same deal. The guy said we broke one of your lugs (which I've become used to hearing by now), we don't have any in stock right now so we'll fix it up next time. Unfortunately I moved in the next month, so had to go to the same shop in my new town for a rotation. After pulling into the bay and hearing the wrenches going, the guy came in and said we don't have any of your lugs in stock and there are 3 more on the same wheel that are tight, so we don't want to take a chance on breaking those.
So I decided to take it to a real mechanic. Turns out he can't get the wheel off at all because the 3 lugs that were "tight" are just spinning. Only choice (or so I'm told) is to cut off the center cap and go from there...which is being done today. $160 estimate for a $2 stud. I'm just hoping that no damage was done to the hub!!