Diagnosis
This is a battery communication fault. The tool's control board is not reading the battery's chip, triggering a lockout.
How to Fix It
Clean the battery and tool terminals with a dry toothbrush or contact cleaner. Press the battery release button and slide it firmly into the tool until it clicks. You must hear a solid click. Try a different M12 battery you know works. If it works, the first battery's chip may be faulty.
If That Didn't Work
The tool's control board or terminal block may have failed from a drop or moisture. This requires a service center. No user-repairable fix exists.
Heads Up
Do not try to bypass this lockout. It's a safety feature to prevent use with damaged or incompatible batteries.