phaser 4500 - sensors on Tray 1 and Tray 2

I have a phaser 4500 and it gives me an error "Out of Paper' even though there is the correct size paper, weight and neatly stacked.  one person suggested that maybe the paper sensors may be the culprit.  Can someone please let me know which are the sensors on both trays, i.e. Tray 1 and Tray 2.

i have tried to setup on the printer, to set the tray sequence from 2-1; and 1-2, but both give me the same error, of Out of paper.  Thus, maybe both tray's sensors may be screwed up.  Thank u.