This error indicates the EMV gateway service is not running in background for Worldpay/Vantiv processing.
To start the service click the NETePay shortcut button on the Windows desktop. You can then minimize the window if required.
If NETePay is not loading normally you will need to save the transaction in progress (Ctrl-F12 Hold), then close POS and restart the PC. Make sure NETePay is running before starting POS. Once logged into POS press F11 Recall to recall the transaction on hold.