During the update from Messaging Gateway (SMG) version 10.5.4 to version 10.6 a data access exeption error is logged to the BrightmailLog.log file indicating that the communication link with the database has failed.
Aug 19 2015 14:48:04 [BrightmailScheduler_Worker-48] [HostSettingsManager] ERROR - com.symantec.smg.controlcenter.internal.dataaccess.DataAccessException: An unexpected database error has occurred. Please contact your system administrator. ; nested exception is:
com.mysql.jdbc.CommunicationsException: Communications link failure due to underlying exception:
This message can be safely ignored.
The error is raised during the update when the Control Center web application attempts to communicate with the database after the database process has been shut down in preparation for the update.