This happened to a client as well: the stock Windows Vista PCL5 driver for an IP-connected HP LaserJet 4050TN would not allow you to select a paper tray. Not for default settings, nor for printing preferences.
The solution: download the HP PCL6 driver for Windows Vista from HP LaserJet 4050 Printer series – Download drivers and software .
LJ 4050n – Can’t select Tray 1 in driver
I have a 4050n connected to a small LAN, with 3 XP-Pro SP2 machines. These all print directly using standard TCP/IP ports. They were installed using the PCL5e driver downloaded from HP ( 4.27.4050.410 12 Dec 2003 ) This all basically works.
The only problem is I cannot select tray 1. The ‘paper source’ drop-down is greyed out at ‘auto select’. Printer always prints from tray 2 ( A4 Plain. )
Try the PCL6 for a 4000TN, the printer still works if a 4050 has a 4000 driver loaded, had similar problems just used the 4000 driver.