WO 4.5 was for Mac OS X Server 1.2 (Rhapsody based OS). Apple has released 4.5.1 for 10.0.x (which is a good thing because 5.0 dropped support for Objective C). You'll need the latest updater to run 4.5.1 on 10.1 (update 3, see http://docs.info.apple.com/article.html?artnum=75175 ).