File is Damaged or Unsupported

I created a bunch of AE projects in CS5 a few months ago. Now when I try to open them in CS6 I get this error:

This is ONLY happening on my Sony XDCAM footage (MP4 wrapper).

At first I thought I was missing a codec or a problem with me running Windows 8 beta, but I can see and edit these same XDCAM files in Premiere just fine. Just AE can't do it.

Any suggestions?