pdottz : search in the direction celtic_druid pointed out : the AVI splitter of Gabest may be guilty. So download the latest version of MPC ( if it's not already done ), and if it doesn't work, make a bug report on the player forum in the thread related to MPC ( the big one

).
It's not an XviD issue ( since you're decoding with DivX5 ).
Furthermore, since you don't seem to have it installed, grab and install FFDshow. And read
this, it will be easier for us to find what could be wrong.