I've had many problems w/ importing Maya camera data into AE as well. Sometimes it works, sometimes it doesn't, it's terribly fustrating. But in case it helps, random things I've noticed that can throw things off:
I think using different units in Maya can produce different results (mm vs. cm vs. inch, etc), same for using a non-standard camera setting in Maya (maybe try 35mm Acadamy?), and I'm not sure why you're even working in non-square in Maya/AE. I always render out 720x540 sq in Maya, interpret video footage and scale to square pixel in AE, the squish it back out to non-square when it's ready for delivery.
It's a shot in the dark but make sure your Maya and AE is updated to the newest versions, I know AE 7.0 had some problem w/ importing .iff files but the update fixed it. And finally you could try the MoCon script, I've used it for getting AE camera data into Maya (works great) but haven't tried the other way around.
http://toolfarm.stores.yahoo.net/3dmov2.html
http://www.3dmation.com/maya_to_ae.html
Let me know if you find a solution.
