What's the difference between uTorrent 2.0.4 and 2.2 ?

Your copy of uTorrent is probably having trouble connecting to the uTorrent server to check for updates. This could be caused by a number of problems including a your firewall, slow internet, heavy load on the server, etc. Since an error occurs during the update check, it assumes no update is available.

Generally a higher version of software means greater stability and possibly new features, but you can know for sure by checking the changelog/release notes for uTorrent 2.2.