Trying to convert an AVI to anything and the process crashes (but sucessfully run before) is a big indication that the AVI has problems. This is VERY common unfortunately. Check the avi with DivFix and DivXRepair or even VirtualDUB's scan for brocken frames.
Also, as said above, I would strongly advise NOT to install any Codec pack, they have killed more systems than they have ever helped. All you need to decode Divx avi's is DivX 5.x & the latest XVID codec. URL's for d/l of these can be found in the Tutorial The Poacher gave.