How do I hook my external laser printer to my humphrey 740?

Sounds like a heat, thermal issue. You may have a non- functioning cooling fan somewhere inside. There are several of them so don't be fooled if you hear one of them running. Same issue happens with CPUs on PC computers. Will suddenly shut off if too hot.

is the cooling fan turning?

I believe "state 19" is a weak main illumination bulb. Not sure if it's the same on your 740, but that's what the problem was with our 750i. Even though the bulb appears to be working, they dim over time and won't pass the start up calibration checks. On ours, there is a round access panel on top of the unit to service this bulb. Just be careful removing the bulb and don't bump any of the clear optical wheels. Part # 2660021106082 (for 750i. not sure about 740) Call Zeiss to confirm. Realize this is an old post so info is for future readers.

erro 99

Here are "little" specification:

Body installation method desktop page printer
Photosensitive medium OPC drum
Exposure method semiconductor laser
Development method Toner projection development
Transfer method by roller
Separation method by curvature
Cassette pickup method by pad
Multifeeder pickup method by pad
Drum cleaning method by blade
Fixing method on-demand
Delivery method face-down/face-up
Toner supply type by toner cartridge
about 6000 prints (A4, single-sided; at 5% image ratio)
Warm-up time in standby: 0 sec (at power-on: 10 sec or less)
Print area top: 5 mm; bottom: 5 mm; left/right: 5 mm (if envelope, top, bottom, left,
right: 10 mm)
Printing resolution 600dpi
First print time 9 sec or less (approx.; A4)
Print speed (A4) 21 pages/min (approx.)
Cassette paper size A4, B5, A5, Legal, Letter, Executive
Multi-purpose paper size A4, B5, A5, Legal, Letter, Executive, Envelope DL, Envelope COM10,
Envelope C5, Envelope Monarch, Index Card, Custom Paper Size (width
76.2 to 215.9 mm, length 127.0 to 355.6 mm)
Cassette paper type plain paper (64 to 90 g/m2), heavy paper (91 to 120 g/m2), recycled
Multi-purpose paper type plain paper (64 to 90 g/m2), heavy paper (91 to 163 g/m2), recycled
paper, transparency, label paper, envelop (DL, COM10, C5, Monarch,
B5)
Cassette capacity 250 sheets (approx.; plain paper, 64 g/m2)
Multi-purpose capacity 1 sheet
Delivery tray stack 65sheets (Face-down) /1sheet(Face-up Output Slot)
Memory 8 MB (internal; no optional memory available)
Operating environment
(Temperature range) 10 to 32.5 deg C
Operating environment
(Humidity range) 20% to 80% RH
Noise 52.8 dB or less (during printing; based on ISO9296; announced noise
emission)
Power supply rating AC100V±10% (50/60Hz ±2Hz)
Power consumption (Maximum) 790W or less (approx.; 20 deg C; for input of rated power supply;
including peak value lasting 1 sec or more)
Dimensions 370 (W) x 375 (D) x 258 (H)mm
Weight printer: Approx;11kg; toner cartridge: Approx,0.8kg(2.5K)
Option paper feeder

It probably wants you to load paper in the multi-purpose tray or pull-down bypass tray

MP Feeder refers to Multi Purpose Feeder or Manual Paper Feeder or just plain bypass feeder. There should be a door that folds down to gain access to your MP Feeder tray. Try loading letter size paper on this tray.

Make sure you have selected the multi purpose feeder (front of the printer) in the driver, not the Manual Feeder.

The manual feeder will prompt for paper on each page. All you have to do is to press the "Go" button.

Any good quality printer paper.