Hi everybody,
That's an old thread but my revelations might help others.
The machine got the Add Paper error. I checked everything according to mentioned above but to no avail. What we did was blower the machine and that was it. The toner got into the paper path sensors. Simply check the sensors one by one by replacing with good working ones.
Don't use an air blower to clean the machine and 90% chances you'll will be in trouble.
God bless you....