If the error still appears:
1. In the Miner configuration screen check the pool URL very carefully. Any error, including spaces, can cause this error.
2. Confirm that your internet connection is stable. Network configurations or security settings in the router can cause this error.
3. If the network is good then please disconnect all the hash boards from both the power supply unit and the controller. Reboot the miner with only the controller connected. If the error still appears then we need to replace the controller.
4. If the error message does not appear with only the controller connected then please run the miner with one hash board at a time. If one of the hash boards is defective please create a repair ticket and return the whole miner to us for repair:https://shop.bitmain.com/repairGuide