Strange conversion results with different directories

I'm getting "conversion failed" messages. I've followed the tutorials except that I have the 3 files going to different directories

users/[user-name]/thumbnails
users/[user-name]/flash videos
users/[user-name]/uploaded videos

I have flashvideo set so it performs the conversion at node creation. It seems to create the directory structure fine, but sometimes the flv conversion fails and sometimes it doesn't fail. Sometimes it tells me there was a failure, but the files get created anyway. Sometimes the .jgp gets created and sometimes a copy of the previous user's .jpg gets stuffed along with it in the wrong user's directory.