http://blogs.msdn.com/astebner/archive/2008/06/22/8639824.aspxWhen authoring deferred custom actions (which are custom actions that change the system state) in an MSI, it is necessary to also provide an equivalent set of rollback custom actions to undo the system state change in case the MSI fails and rolls back.en-USCommunityServer 2.1 SP1 (Build: 61025.2)