Hi, Our new 3CX Server (v12 with sp6; .net framework 4.5.1; Windows Update up-to-date; Windows server 2008 R2 Enterprise) had below issue twice in a week: All 3CX Window Clients display 'NOT CONNECTED' under 3CXPhone mode, Looks connected under CTI mode but the Queue option and Availability option are all greyed out , IP Phones were working fine. Checked '3CXPhone Clients' and 'Server Event Log' attribute, the windows clients are all registered in the server. We tried to recycle Application Pool or restart IIS service, did not have any luck. Then restarted the 3CX PhoneSystem service which rectify the issue. There is no obvious error message from window application log and system log, Server Event Log and Server Activity Log all look normal. Since We are using the server for a contact centre environment, we could not have enough time to test which particular service cause this issue by interrupting the operations, and the issue really cause trouble because we need the Windows Client to trigger screen popout for particular software. Please advise.