Unable to play certain video files from Seagate Expansion Drive in F Row

I transferred all my H264 MP4 videos files from my 320GB Western Digital portable hard drive to a 500GB Seagate Expansion portable drive.

However in Front Row, only certain video files will play in Front Row from the Seagate. The ones with a higher bitrate play fine, but not the lower ones. But they play fine in Quicktime.

In addition, if I revert to the WD drive, Front Row plays all the videos fine, even the ones Front Row had problems with on the Seagate.

Does anyone have any ideas why this is so?

Thanks in advance

Paul