You should check with someone else with the episode though to make sure the file just isn't encoeded poorly, because if thats the case not much you can do.

If your computer isnt fast enough to handle decompressing the file, then a player that requires less resources would be your best bet. (This is probably not the case if your other files play well)

And If the problem is the codec you will simply need to try different versions.

I actually use to have problems with some Naruto eps where there was blockiness around motion after i changed from divX 5.02 to 5.05. but was resolved after I downgraded back to DivX 5.03.