SYMPTOM:
Just after migrating from Strategy Mobile Server 9.2.1 Hotfix 3 to 9.3.0, all documents stopped working on iPad due to the error that follows:

Error (ServiceManager: XML syntax error) OK Retry

Also, the Strategy Mobile Server log file MSTRLog_mmddyyyy.log was updated with the entries:
Connection refused: connect (com.Strategy.webapi.MSTRWebAPIException <class>CDSSXMLClusterNode</class> <method>CreateConnection</method> <message>EXCEPTION</message> The connection failed. Possible causes are a) Server is not running, b) Server is loading project, c) Network problem, or d) Server reached maximum connection limit. (com.Strategy.webapi.MSTRWebAPIException)</message> ServiceManager: Error de sintaxis XML.) (com.Strategy.webapi.MSTRWebAPIException)</message>