HP LaserJet "Load Tray 1 Plain Letter"...print to Tray 3?

Hi all,

Have a HP LaserJet 4515tn. Tray 1 is the fold out/bypass, tray 2 and 3 are 500-sheet drawers.

Tray 1 stays shut with no paper, unless someone needs to load special paper in there.

Tray 2 has preprinted form A loaded.

Tray 3 has preprinted form B loaded.

I've set each tray as letter-size, but each one has a different type of paper. IE: 1 = Plain, 2=Letter head and 3= Cardstock.

This used to do the trick, as we have an application that prints to the pre-printed forms to the specific trays...but now, when I try to send a job to tray 3 from the program, the printer reads "Load Tray 1 Plain Letter."

Any ideas on how I get this tray behavior to work again? I've mirrored the settings on a (working) 4350tn, but I'm obviously missing a step somewhere.

Thanks!