I have had a HP Color Laserjet 3525 printer for several months, and just recently it has started asking for me to manually feed paper every time I print to it.
There are two trays, Tray 1 has legal sized paper and Tray 2 has letter size. Both trays are full, and they are both configured on the printer as having the corresponding paper type.
When this started occurring, no settings had been changed on the workstation previously. The Paper Source option under Printer Preferences was previously set to "Automatically Select". I have since changed this to "Tray 2" to avoid having to walk over to the printer every time I want to print, but this only works for letter sized documents. I am unable to print legal sized documents now without having to go change the printer settings first (and would much rather it return to the functionality of automatically choosing).