Do any of your frames include transparency? (The frame shown, with the grey background, appears as though it might.) GIFs support index transparency but not alpha transparency, so any semi-transparent areas make use of a matte color. I'm wondering if the white patches might be a matte color substituting for partially transparent pixels.
Also, I'm not sure how transparency is handled in an animated GIF.
Thanks Groove, it was the transparency! I exported with no transpaerncy and added a matte background and now all is well. Because it looked OK on half of the emails that we sent it too, I was hung up on thinking it was file size or some other issue.