A sheet driver for use in a drug dispenser where the sheet driver includes a shaft with a shaft cavity co-axial with a rotational axis of the shaft and a hub that defines a hub aperture, where within the shaft cavity there is an indicator pin having a side member and an indicator pin head that may project through the hub aperture, where within the shaft cavity there is a spring for biasing said indicator pin out of the shaft cavity, and where an engagement member may selectively engage said side member of the indicator pin to prevent movement of the engagement member upon the occurrence of an fault condition of the sheet driver.