I doubt you need to clear. With the door open push the test button on the MPU. Scroll thru the option to the machine options. Find the bill validator and try to enable it. With the sentry system you have it is telling you the BV has a problem. I am going to guess you have a WBA BV so remove it, open the transport, and front to inspect for a jam. I have found quarters shoved in by kids, blocking the optics thus a problem. Most often removing/replacing the BV will make it cycle. Normally replacing the cash can will make it cycle also.