Maybe an XVid encoded AVI?
If so you should
either set DivX (if 5.1.1.) "Quality setting" to "Support Generic Mpeg-4" (through [Start] > Programms > DivX > DivX Codec > Decoder Configuration Utility ....
or you should download/install a more recent version of XVid codec.
See
adocoto's post
here.
(P.S. For GSpot or Avicodec look under item 2 of my
Help to Help post (link hereunder))