Suppose You have four load generators each generating 100 Vusers.You are seeing that 400 concurrent Vusers are running and few transactions are failing due to UCF communication problem. So what might be the root cause?
Loadgenerator are unable to communicate with the Controller.
UCF Invoker is not running one/few of the four Load generators
Loadrunner Agent Process is not running.
Web Server is unable to process the requests.