(running a perfectly stable Win 98, no probs with all files, except

2 XVID avi files (one with mp3 audio, the other with ac3). upon opening virtualdub, i receive "-100" error (general error). files are supposed to be perfectly encoded, but they're uneditable and unwatchable with any of my media players - they simply crash, or sound is ok but no pic.
divfix or any other fixing program came with no help.

so, i managed to access the files after changing their fourcc code to DIVX or DX50. great, vid frames look nice with virtualdub. extracted the audio separatly, no probs. then i mixed them easily with vdub. i get a proper divx avi file:

vdub scans NO errors, NO bad frames whatsoever
vdub mp3 freeze scans NO freezes
divfix finds NO errors
audio runs smooth

BUT...

no movement with the video. all i get is running audio and still images, sometimes jumping ahead, sometimes just stuck.

only player that runs the movie perfectly is Divx Player, exellent, with perfect synch.
all other - windows media player (6.4), avi preview, Vidomi, and my standalone dvd divx player (Vertex 312a, which plays ANYTHING) - simply stuck. just audio, and un-moving movie.

any clue?
help would be appericiated!