Reason 4 is a Universal Binary application, and can only be ReWired to a Universal Binary ReWire host.
Hence, running Reason 4 on an Intel Mac requires that you run a Universal Binary version of Logic. Logic is UB from version 7.2.1. If you haven’t updated to Logic 7.2.1, please visit Apple’s web site to download it. If you’re already running Logic 7.2, the upgrade can be fetched and installed by running the System Update application.