Yeah, that's odd. I'd say double check thru your time line to make sure there isn't something there throwing it off. Are you actually rendering the avi or is a preview playing oddly... I think there is an issue there (have seen this) so if so use something else to play the actual rendered movie and double check frames on the movie render. The other possibility may be to close carrara out to removed cached info or start over if you can't locate something in the timeline or file that might be causing an issue. The timeline is quite deep.

No need to think outside the box....
    Just make it invisible.