PrPro Projects will not open in PrE. Some PrE Projects will open in PrPro, like simple PrE 4.0 Projects will open in PrPro CS2.
Thanks for your quick answer.
You are most welcome, though it's probably not the answer that you wanted.
There are just so very many differences between the two programs. As a test recently, I took a PREL from PrE 8, IIRC, and it would not even open in my PrPro 2.0, like my simple PrE 4 Projects would. That PrE 8 test Project was also simple, with no Themes, or Instant Movies - just Cuts and some common Transitions, no Effects. Just too different to Open.