HP Color LaserJet Enterorise M750n Optional Trays

Dear,

I bought QTY: 10 HP Color LaserJet Enterorise M750n (D3L08A) and also bought for each printer two optional trays (CE860A).

In the scond page of the attached brochure, you will find that I can add up to 2 optional trays to the printer.

I add the first tray and there was no problem.

When I try to add the second tray, I got the message " not supported"

Please Advice.

Regards.