I'm trying to render a video into the lossless preset. Kdenlive shows render is complete, but when I try to open the generated avi file, I get this error message: "Internal data stream error.". Any help would be appreciated as I'm lost as of what to do. I'm running Ubuntu 10.10.

try these settings (Authur sucks uses them)
use the FFV1 codec in a MOV container.
profile settings
Group:Lossless/HQ
profile FFVI
extension MOV
parameters box put in this
acodec=pcm_s16le vcodec=ffv1
qscale=1 aspect=%dar