This error is caused when the milling PC loses connection with the milling machine.
Here are some common solutions to solving Runtime Error 8018:
1. Disconnect and reconnect USB cable from PC and the milling machine
2. Ensure you have a direct connection from the PC to the milling machine (USB hub not recommended)
3. Restart PC and milling machine
4. Ensure your USB cable is less than 3 meters
5. Ensure the power cable and USB cables are not tangled / twisted together
6. Ensure your PC does not go into Sleep or Hibernate mode during milling.
Related Article: Disable USB Selective Suspend Setting