Most often, "imaging blank film" is happening because some foriegn material is blocking the laser from hitting the film.
The machine "knows" if the laser is working, and will post an error if it is not.
It "knows" if the scan mirror is spinning, and will post an error if it is not.
Most imagers have no clue if the laser is actually making it to the image plane tho.
Perhaps:
The last time the imager ran out of film, a scrap fell somewhere it shouldn't be.
Less likely, but possible would be:
Wrong type of film
Film installed in the cassette incorrectly (upside down)
Another that is only possible on some machines (autologic 3850 for one) is that a door is open but the machine is configured to ignore it. Open doors will generally cut power to the laser.
