Topology Discovery failed 0x80040a02

-At the domain controller open Active Director Users and computers.
- Right click on the domain container and click on properties.
-Click on the Group Policy tab, hi-light the default domain policy and click on the edit button.
-Expand the default domain policy tree: Computer configuration, windows settings, security settings, local policies, user rights assigned.
-In the right hand pane open the “Manage auditing and security log” policy.
-In my case I had to click on the Add button then the browse button, then find and select the ôExchange Enterprise Serversö user.
-Restart the Exchange server and things are working again!