Can you create a test Project in PrE 9 and does that work. If so, close that Project and then Open it again in PrE 9.
It could be as simple as your PrE 8 Projects just not Opening in PrE 9. There is often forward compatibility, but not always. It is usually best to finish Projects in the version, in which they were started.
Many on this forum, myself included, strongly recommend against opening older version projects with a newer version of the program anyway.
It often leads to buggy behavior.
So, if you do succeed in doing it, be sure to keep a copy of the old version project file around just in case.