same thing happened to me Jen. I was getting "wrong codec" or some biz and gave up on the AVI.
What i did do to counteract it, (as suggested by our JJJ

) was to make an image sequence of the AVI movie, and stack those images. It might be a tad more work but at least i got a result.
I used VideoPad Video Editor to create the image sequence, then AVISTACK 2 to stack the images with varying results.
From my experience, Registax v 5.1 was better to do the Wavelet sharpening with. V6 keeps crashing