Originally Posted by Shawn76

Since this is on an Exchange Server, you may want to check with your admin to see if they disabled the feature for some reason.

Found this in another post:

http://support.microsoft.com/kb/q258277/, is a link to microsoft saying to add the entry to disable pst sharing, so a natural assumption would be to delete it, to restore it. However, if it is implemented as part of domain policy then it will just reset with the next boot.