The error message "searching inv check line plz" indicates a communication issue between the control board and the LCD keypad. This can be caused by a damaged cable, a bad keypad, or a faulty control board.

To troubleshoot this error, you can try the following steps:

1. Check the cable on the back of the keypad to ensure it is not damaged.
2. Swap out the cable if possible. The cable is a standard straight-thru ethernet cable.
3. Swap in a known good LCD keypad.
4. Replace the control board if the above does not work.