What is the solution to a printer when a message like 21.1:03 appears on the screen?

Need more information. If the error message appears on the display panel of your printer/copier then you will have to refer to the printer/copier manual. If it appears on your computer screen, it may come from the printer software or the operating system

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Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/normanj_7893313f0751935f

Each cartridge having printing life, as long as cartridge health condition is good it won't gives any trouble. Subjected series printer having mono & colour cartridges,1. Remove both cartridge from the printer 2. Switch on & wait till message appears for insert the cartridges..3. Insert mono(Black) cartridge, close the door & wait till message appears on screen. If message appears same as cartridge error mean that mono cartridge is faulty replace it, if message appears like insert another cartridge, it's confirmed that colour cartridge faulty.. Replace it..

The 1201 error message could indicate a serious hardware failure. Try to power the printer off > remove all cables from the back of the printer > re-insert the power cord > switch the printer back on and check if the error re-appears on the printer display screen.
Should the error persist, please contact Lexmark Technical Support Center for additional assistance.

The only fix that I know is to get the scanner/copier assembly(that's the assembly at the very top where the copier is) replaced.
I don't imagine that it is cheap. Get an estimate 1st.

It could be a communications error message, the printer is not communicating with the computer.

Disconnect and then reconnect the USB cable.

Disconnect and then reconnect the printer power cable.

Restart the computer.

Remove and reinstall the printer software

If your printer does not function properly or communication error messages appear when using your printer, you can remove and reinstall the printer software.

1. Click Start®Programs or All Programs®Dell Printers®Dell Photo AIO Printer 962®Uninstall Dell Photo AIO Printer 962.
   
   
2. Follow the instructions on the computer screen to remove the printer software.
   
   
3. Restart your computer before installing the software again.
   
   
4. Insert the Drivers and Utilities CD, and then follow the instructions on the computer screen to install the software.
   
   

If the installation screen does not appear:

1. In Windows XP, click Start®My Computer.
   
   

In Windows 2000, double-click My Computer from your desktop.

1. Double-click the CD-ROM drive icon. If necessary, double-click setup.exe.
   
   
2. When the printer software installation screen appears, click Install or Install Now.
   
   
3. Follow the instructions on your screen to complete the installation.
   
   

Communications error message
The printer is not communicating with the computer.
Communications error message
The printer is not communicating with the computer.

Hi juniorgona:

15,004.45:
TCD_THERMISTOR_
SLOW
Most likely cause is a failed drum heater. The head to drum gap
should only be checked or adjusted on the Phaser 840. The
Phaser 850 and 860 have a pre-adjusted head.

Hope that this helps.

The error code refers to Ink Cartridge

Issue: ERROR: Error code 5100 appears on the computer screen
Issue: ERROR LED: E, 2, 2

1. Disconnect and reconnect power cord to reset the device
2. Remove Packing Material MP160 / MP180 / MP460
3. Reseat ink cartridge (MP160 / MP180 / MP460)

Copy function was not working, says "device is busy". Message appeared on the printer screen is:"scanner error 5, turn off then on". This was done several times and message still appeared. I called 866-625-1176 and was connected with HP Technical Support and after 20 - 25 minutes of diagnostics, the technician informed me that they were sending me a new printer at no charge. I assume this meant that HP is aware of the defect and has no solution other than to replace it. The printer was only 6 months old.