Sounds like AE doesn't like the file format or video codec being used.
Try converting your MTS file to a lossless Quicktime before importing to AE.
AE 10 seems to have solved the problem you're having; unfortunately, you run AE 9. Thus, the following cut 'n paste response I use on the Creative Cow still applies:
Dave's Stock Answer #1:
If the footage you imported into AE is any kind of the following -- footage in an HDV acquisition codec, MPEG1, MPEG2, AVCHD, mp4, mts, m2t, H.261 or H.264 -- you need to convert it to a different codec.
These kinds of footage use temporal, or interframe compression. They have keyframes at regular intervals, containing complete frame information. However, the frames in between do NOT have complete information. Interframe codecs toss out duplicated information.
In order to maintain peak rendering efficiency, AE needs complete information for each and every frame. But because these kinds of footage contain only partial information, AE freaks out, resulting in a wide variety of problems.
I'm a Mac guy, so I like to convert to Quicktime movies in the Animation or PNG codecs; both are lossless. I'll use Apple's Compressor, Adobe Media Encoder or Quicktime Pro to do it.
im hoping to upgrade to cs5. unfortunately right now all i have is cs4. i have tried converting the footage but to be honest its very grainy. i can always export the files and re-import but its very cumbersome.
i can always export the files and re-import but its very cumbersome.
It would appear you have two choices:
1) Export files in an intraframe codec, and re-import into AE.
2) Blow it off and continue to get error messages.
One way gets the job done, one way doesn't.