Thanks Steve. I would be interested in learning if you can recreate this issue. One other thing I have tried since my post is to try and play the MPEG 1 file created on my Vegas pro 11 machine on a different computer (the one that host Vegas 8) in its windows media player and it actually plays fine.
So to recap if i create a MPEG 1 file in Vegas 8 it plays fine on the Vegas pro 11 machines WMP. If i create a MPEG file in Vegas 11 pro it wont play back in WMP on the same Vegas pro 11 machine it was created on (Windows 7 64bit) but it will play back fine on another computer (32 bit windows XP machine running Vegas 8). For some reason WMP on the new 64 bit windows 7 machine doesn’t like the MPEG 1 render coming from Vegas pro 11.
I should also mention that I have tried turning off the gpu rendering support just in case that was doing something different to the mpeg 1 render (like a slightly differnt variation of the mpeg1 encode)thinking that might have been the culprit, but that didn’t work, still get the error when playing the file back in WMP on the 64 bit machine it was created on.
What i may have to do is install pro 11 on the other 32 bit machine and see if the same problem materializes. Your right i will render all MPEG 1 files in Vegas 8 until i can figure this out. The goal though was for me to be able to donate this machine that had Vegas 8 to a charity group i support inorder to teach young people the tools of video editing so i am hoping to get the problem resolved soon.