The update Rollup 4 for Exchange Server 2010 Service Pack 1 has been removed from the Microsoft Download Center. The reason for this are problems with the update, when moving folders it can happen that the content of the folder is deleted.
The problem is to be fixed with update rollup 5, which is expected to be released in August.
If you have already installed the update, you can contact Microsoft Support to get a fix.
The complete article can be found here:
http://blogs.technet.com/b/exchange/archive/2011/07/13/exchange-2010-sp1-ru4-removed-from-download-center.aspx
