[Michael Mueller]

Hi there,

as I had the same problem (I/O error) with the latest CS5 premiere/media encoder I encountered my virusscanner as the origin to the problem.
So deactivate your virusscanner (in my case Kaspersky Internet Security 2011) and see if it helps.

In my case it did. Everything worked fine.
Next step is to tell your viruscanner to perform no checks on the programs like media encoder.

hope it helps…

all the best
Michael