Had some trouble with a case today that the application catalog would not start. When we opened the catalog they could not connect to the catalog service and got this error message. According to the error message it could not connect to the application service.
If we checked the service with ConfigMgr console we can see that Application Catalog Web Point has status Critical
So when we checked the latest events for that components.
As we can see here WCF is not activated, so make sure that WCF is installed,
So after the component in installed try to reinstall the Application Portal Catalog point and it should work 