Operations in Plesk fail intermittently with error:
ERROR: Zend_Db_Adapter_Exception: SQLSTATE[HY000]  An operation on a socket could not be performed because the system lacked sufficient buffer space or because a queue was full.
The server is trying to establish an outbound TCP connection from a port with a number greater than 5,000. Usually, this behavior is triggered by the existence of too many open outbound network connections on the server.
Reconfigure the server to increase the maximum number of TCP ports from which outbound connections can be established. Instructions can be found in the Microsoft Knowledgebase article KB196271 .