I've spent hours and hours trying to get CS4 to open saved projects. Thought I had it handled at one point but alas! I finally figured it out. I had set up my project folder on a new drive but it wasn't set up correctly. By default it goes Premiere Pro> 4.0> and then the projects. I was missing the "Layouts" folder. Anyway I set it up like it normally would by default and it worked!