In first instance you are just changing the media container, but not the codec. Probably VirtualDub can not decode that codec which is in your original toto.mov
container. You can transcode the codec to MPEG-4 with the -q:v
set to 1, this results in good enough quality.
ffmpeg -i toto.mov -q:v 1 -vcodec mpeg4 -y toto.avi