Hi
I have just fallen foul of this too but on a Windows 7 machine running CS4.
It looks like the MJPEG files that the X7 generates are less standard than Prem can cope with even though After-Effects can. Also VLC media player is not happy with them (saying they are broken) but can repair and play them.
In theory you could install a MJPEG codec (
PICvideo ,
Morgan ,
Main Concept ) although I didn't manage to get a demo version of any of these to work - I didn't try very hard.
I took the pragmatic view and transcoded in After Effects. I found the best format, for me, was Quicktime MPEG4 set to best quality and keyframe every frame. This gave me a file with no visible artefacts, only double the size of the original that rendered FAST (about double real time on my machine) and that played beautifully in Prem.
I also decided to apply a little noise reduction and grading in AE even though that increased the rendering time from 2seconds per second to 2 minutes per second, I only have a few file to do so can leave them overnight to complete.
Hope this helps the OP or another stuck with the same problem.
If anyone else has a solution it would be good to let us know.
Good Luck
Mike