vobsub subtitle not working after transcoding

I ripped my movie to .avi with "autoadjust, medium framesize HQ resize" and
separated vobsub subtitles without getting any error message but the
subtitles don't work. Don't know what I am missing. Odd enough the subtitles
are displayed properly when I use the "View vobsub" button and the .idx/.sub
files seem to be created correctly.

Playback with mplayer -v -vob ... gives: "SUB: Could not determine file
format"

Playback with vlc let it close immediatly with "[00000308] vobsub demuxer
warning: reading new track failed" "Segmentation fault"

Playback with kaffeine produces something like "[NULL @ 0xb5a786e8]picture
size invalid (3120627712x64)"


Any hint is highly appreciated!!!
Regards,
Niklas

P.S. I'm using Ubuntu 8.04 with dvd::rip 1:0.98.6-0.0ubuntu1