Hi pcmatty,
I really have no idea if this will work, but perhaps if you convert the video to some other format and then convert it back to .avs (assuming your software can do that) then the message will go away because that program will no longer be the one that did the last conversion. Then again, it may convert the popup messages as well because they may be permanently recorded into the video by using that unregistered software the first time. I'm not sure, but perhaps it's worth a try.
I hope this helps.
Good luck!