Sometimes a Lync Common Area Phone won’t automatically log in, but works when you manually log in. Also you get this error at login:
Certificate web service cannot be found. Please contact your support team.
The certificate web service error is caused because you have spanning tree enabled, causing a DHCP discovery timeout. The Lync Common Area Phone finds itself stuck in a waiting state and never gets to the stage where it can find the certificate web service.
To fix the Certificate web service cannot be found error, enable PortFast on the switch.