What are the Audio specs. of those files?
Are they consistent (is it always the same files that work properly and the same ones that don't)?
Do analyze them with GSpot and post the images here. That will also answer Bill's question about audio formats.
Insanity is hereditary, you get it from your children
Do you have a trial version of PrE9? There was a known issue with the trial version, and Adobe even supplied an updtae to fix this. Have you tried updating the app?
I have the full retail version of PrE 9, purchased from Amazon. I also checked for updates, and PrE says that the software is up to date. Do you think there would be any benefit of uninstalling and reinstalling?
No. You need to do what Bill and Neale recommend or respond to their questions.