The Xsan 1.1 CD includes an "Uninstall Xsan.pkg" file that, if run, will remove files that are essential for serial number verification in Mac OS X Server. If this happens, the next time you restart the server, Server Admin will report that the server is using an invalid serial number.
If you need to uninstall Xsan 1.1 from a computer running Mac OS X Server, or if you've already run the Uninstall Xsan.pkg from the Xsan 1.1 CD, please contact AppleCare for assistance.