I just recently switched to the Mac platform and I installed Reason 3.0.4 on my Powerbook. After installing, I can play the demo song that it opens by default but I can't open another demo song, I can't open any patches from any of Subtractor, Dr.Rex, etc. It gives a "File not found - The Operation could not be completed because a file could not be found" error. I can't do anything really. Mine is a legal registered copy. I tried re-installing a couple of times. All the refill files are there. I tried verifying access, deleting the Reason preferences file. Nothing works. I'm on OS X Tiger 10.4.2.
Are the Refills in the Reason-root folder? I have had a little trouble before with songs locating refills and samples if the Refill gets moved. Since this is a fresh install and you are playing a demo I would assume all should be where it originally was. IF anything has been manually moved, you might run into issues.