Should a 'spanner' (otherwise known as a wrench) icon be displayed in the MMI, it indicates the pen has encountered an unrecoverable error state, thereby requiring it to be re-flashed with the latest firmware.
Download the latest firmware release and install as per the associated instructions. If the problem persists, run factory reset and then repeat the installation.
Pen entering an unrecoverable error state
All firmware versions
spanner, wrench, error, pen unresponsive