A firewall blocking access either on the PC or on the mainframe
An incorrect host name
Wrong port number
Resolution
To resolve the problem check:
The local PC and mainframe firewall to see if they are blocking the connection, the IP address or port number.
The host name specified in the ODBC data source is correct.
The Port Number specified in the ODBC data source matches the port number specified in the mainframe server started task SVDBSPR. The port number is specified in the TCPIP_PORT parameter. The default is 5465. Check the SVDBSPR started task for the port number specified and also for any other error messages.