Change the FourCC code back to XVID, uninstall your current xvid codec and install the latest Xvid codec from http://roeder.goe.net/~koepi/xvid.shtml if you dont have that version.
Load the avi into VirtualDUB and under Video select Scan Video Stream for errors. Set the Video & Audio to Direct Stream Copy, then hit Save AVI. That sometimes helps.
You can also try DivFix to repair the avi.