Some of the users reported that their Communicator/Lync Presence in outlook stopped working.
On further analysis it is found that users have installed another IM client (Cisco Jabber) for testing purposes.
There is a registry key that gets set when another IM client is installed.
We have uninstalled the Jabber client & then reset the reg-key back to Communicator as shown below to fix the issue.
restart both outlook & communicator in the end.