Xerox Versant 180 2100 Paper Tray Doesnt say empty

[azehnali]

I have a couple of versant 2100 and 180 that the tray never says its empty
when you close the drawer with no paper in it it goes up
I have change one tray present sensor and it worked but I have changed the sensor on two other machines and it still thinks there is paper present
anyone have any idea why
thanks