Samsung 2525W laser gives error message "cover is open"

SOURCE: Document Cover Open

I had the same problem with mine. Lift the top scanner, and check the hinges on the left. That error message means that the little black sensor on the left next to the hinges is not meeting flat with the unit when closed. Hold the sensor in for a few seconds, and your printer will start working properly.

SOURCE: error message inner cover is open canon pixma mp610 printer

Had the same problem myself but discovered that I had previously moved the inside flap down when I put the ink in. I moved this back into position and bingo! (If you make sure all the covers are closed then look into the printer where the paper exits you will see the flap that moves up and down, this must be in the up position)

SOURCE: Our HP Color Laser Jet 4700 dn frequently gives an

There is either a small piece of paper in your paper input section or you have a paper sensor going bad.

SOURCE: my laser printer gives message open heat error

This is most commonly caused by a failure of the Fuser unit.
However, in rare circumstances, this can be caused by the Fuser Control section of the SMPS, or the fuser temperature monitoring circuit on the Main Board.
There is a closed control loop:
1. AC voltage is supplied to the Heat Lamp in the Fuser from the Fuser Control section of the SMPS
2. The temperature of the fuser heat is monitored by a thermistor (mounted on the Fuser) connected to the Main Board.
3. The Main Board determines if the fuser temp is too low, correct, or too high and signals the Fuser Control to increase, maintain, or decrease the AC voltage to the Fuser
sorry io say but you had to replace the fuser
call dell costumer support and tell your model no. ask for fuser replacement and they will do it .
Hope your printer is in guarantee period otherwise you had to pay.
REGUARDS

SOURCE: Samsung ML-2525W monochrome laser printer;

I have the same problem with mine - first job usually prints but no go on the second one. It tells me the printer is "offline". In some cases I can't even power cycle normally. I have to unplug the back cord and plug it back in, then I can power back on.
I called Samsung today 1-800-726-7864 and was told the printer will need to be taken to a repair center for service. Wish I had better news.