I continually was receiving "Paper Jam 1" error on my Samsung SCX-4016 "Flatbed Laser Multifunction" Printer. Even when it was clean of jams, the error would come up every single time when trying to print.
The problem was the lever/flag that determines the paperjam fell out. It wasn't broken or bent. I wasn't moving the machine or using heavy paper. It just fell out during normal use.
Here's how to fix the problem
Remove the 4 screws in the back holding on the darker plastic casing.
Locate the jam sensor and the lever. Once the back is removed you should be able to see the circuit boards. The 'U'-shape jam sensor should be located in the center of the machine just under the rollers. Normally the 2-inch lever should be sticking up above that. The lever should reach from the sensor to a little higher than the two sets of rollers above it. My lever was just laying on the circuit board.
Snap the lever back in. The lever should have round pegs on both sides and you should be able to see the brackets the pegs snap into. The tricky part is the narrow end of the lever has to go upright BEHIND (looking from the printer back) the first set of rollers and the fat end goes INFRONT about where the sensor is. The spring will be on the left and there is a little indent. Spring tension should be just enough to keep the narrow "roller" end away from you, and the fat "sensor" end toward you and out of the sensor (when paper comes toward you, the top comes toward you and the lever bottom moves away from you and between the sensors).