Users migrated from OCS 2007 RTM version to R2 version will get an error that all contact’s presence is “Unknown”

Cause:
—–
Local cache of MOC client problem. MOC failed to update current status of
contact.

Solution:
—–
Delete local cache.
Location is
(Vista/2008)
“%userprofile%\AppData\Local\Microsoft\Communicator”
(XP/2003)
“%userprofile%\local settings\application data\Microsoft\Communicator”.