Yes, I tried verifying the file cache earlier. Thanks for explaining the command line numbers. I didn't realize it was just the same thing as altering the permissions the other way.
I also got Shattered Haven, but I haven't tried it yet. But I expect it will be the same thing, if it's built using Unity as well. As I said, the Tidalis demo worked fine, but the Steam key doesn't work with it, for some reason. If I don't hear back from you sooner, I'll try moving them out of the SteamApps folder, to see if that helps.
Oh, and I came across another support thread that suggested that disabling the Steam Overlay would help with similar problems. It didn't, in this case, at least with Tidalis. Haven't had a chance to try it yet with the others.