Since the latest release once again the craftbukkit does not work unless you install one of the latest dev versions. Once we get a stable release we'll add it to the mod section on the server control panel. To update your current server follow these directions:
Download the current craftbukkit-SNAPSHOT.jar from your server just in case you need to revert back. Download the latest build snapshot, rename it to craftbukkit-SNAPSHOT.jar and upload it to your server via ftp. Make sure your server is stopped while doing this. Here is the link to the latest dev builds:
http://repo.bukkit.org/index.html#view-repositories;snapshots~browsestorage