No GAL synchronization is taking place, QCS status messages are accumulated in the service mailbox. At the same time mailbox is passing TEST successfully and can be accessed via Outlook while authenticating as QCS service account. The following warning is frequently appearing in QCS Events log:
Warning 32622. Exchange Layer. Error occurred while retrieving data from the Exchange server. [0x80070534 (No mapping between account names and security IDs was done.)]
Local Administrators group on QCS server was renamed.
Upon QCS Synchronization Service start up it verifies that permissions are set as required on internal QCS application COM objects. This is done via local Administrators group. If renamed, it can create inconsistency within the COM objects permissions model which QCS relies upon, causing it to stop working. Please rename local Administrators group back to the default name and restart QCS Synchronization service on the server where it is installed.