I'm not really familiar with the Salesforce Connector. But most Qlik Connectors generate logging information about their activity somewhere - possibly in a dark place. And even when used from QV Desktop. Can you check those logs whether they contain any additional information about this issue?
We are having similar issues, the v11 SalesForce Connector stopped working. When we try to use the new connector (v14.1) we are getting the same error 'The selected connector has stopped running and has therfore been disabled'.