When able123 mentioned FireWire 800 something popped up in my head: FireWire 400/800 and large file transfers = Problems.
The background is that the FireWire drivers in Win 7 fails when you transfer large files, and the result you get is that files won't open in Premiere Pro since the files/s has been corrupted during transfer. It happened to me everytime i transferred media from a Canon XF100 camera via a FW800 CompactFlash reader. When i changed the driver, every transfer has been problem free. 
You can either go to http://www.unibrain.com/download/download.asp and download their drivers or fix it manually in the Device Manager: http://avid.force.com/pkb/articles/en_US/Troubleshooting/en370145
You need to transfer the files from the external HDD, again.
I would start to roll back to the Legacy driver manually and transfer one (1) file from the external HDD to the internal HDD to test.
I had many issues with files from the XF100 when i transferred files via FW400 or FW800. None of the files would open in Premiere Pro until i changed the drivers and re-transferred the files.
/Roger