There are several common causes and solutions:
1. Possible Cause
The Power Meter address is incorrect
Possible Solution
Check that the Power Meter is correctly addressed, each meter on the same bus should have a unique address.
2. Possible Cause
Power Meter baud rate is incorrect
Possible Solution
Verify that the baud rate of the power meter matches the baud rate of all other devices on its communication link.
3. Possible Cause
The parity is incorrect
Possible Solution
Check the parity on all the meters are the same on the communication link.
Note: This is not an extensive list, for example; it is always good to check if the physical cable and connections are healthy.
Another approach is to check another meter, and complete exclusive tests to identify the fault