ag_UnitFrames problem
 

Hey guys,
small problem here. ag_UF is working but from time to time it pops this annoying error:

http://x.pbf.hr/~phiber/error.jpg

If anyone can help me, would be much appriciated. I don't know if this deserves a separate thread but a lot of people from my guild switched to this Raid wise and a lot of them have this error. Thanks in advance.