Tempgenc: no joy with ac3:

tempgenc cannot open c:\xvid-ac3 {I-S}\movie avi.avi as an audio file.

after i have selected the source, i get the above error.
the file is ac3,448 kb/s (6 ch) CBR ,AC3 (0x2000),ac3 (0x2000) Dolby Laboratories, Inc.

i have tried ac3, dr divx but no joy- please advise.

Demux the audio stream using VirtualDubMod and encode only the video.