Just a guess, but there were known issues between MediaStudio and Version 6.5 of premiere. I am not aware of any issue between Mediastudio and Premiere Pro. having said that it may be worth downloading the pacth (for Media Studio) to see if that resolves the problem. Incidentally I understand that Mediastudio uses Main Concept decoder in all its products.
The link (MPEG Vio Update) is at the bottom of the page, http://www.ulead.com/tech/msp/msp_ftp.htm
As I say it is a long shot, but you never know!
COMPAQ something or other with 500Gb Boot Disk, 1Tb external Firewire Disk, 4Gb Memory and a super duper sound card, 19" TFT Monitor etc etc etc
Sony TRV33e : Sony TRV310e : Canon XM2
Sony Vegas Studio editions to v11
Remember, there is always more to learn than there is to teach.