I had the same problem as you. A quick Google search revealed that others had the same issue, but I didn’t find any one who had reached a resolution. Perplexed, I strolled over to my coworkers suite and tooled around for a few minutes and discovered that he had several more files in his /Library/Application Support/ProApps folder. Most notably I was missing a file called Soundtrack Pro Integration.bundle inside the Bundles folder of this directory. I copied the files over to my system and restarted FCP. Everything appears to be working now.
My system had been upgraded. (Knowing full well a clean install would have been better.) Perhaps it was a problem with the upgrade or a faulty update along the way. At any rate, I suspect that if you don’t have a coworker that you can steal these files from, a clean install of FCS should fix the issue.
Chris Phillips
The Videohouse, Inc.
Pittsburgh, PA