[Wayne Bertram]

Had the same problem here.

Premiere can not handle these files at this stage (the 50Mbps files). I got a mate with Vegas Pro 8 (which handles the files natively) to import them and them export them into a format I could use. This is the only workaround I know of unless someone has a better solution. Maybe a trial version of Vegas would do the trick for your project this time.

Hope this might help

Wayne