Laserjet M401dw Output Bin Full Message - Solution Needed - Can I Replace the Sensor?

I have a Laserjet M401dw.  I keep getting the "Output Bin Full" error message - but there is not paper in the bin.  The black plastic output lever moves freely and is not broken.  I need a solution.  Should the sensor itself be replaced?  Where can I get the part.

Thanks!