A common problem for older the ImageWriter II is that it continues to print after the paper has run out. The fix is easy: Replace the platen or use a solvent such as Fedron to clean the platen surface.
This works because the optical sensor assembly relies on the reflectiveness of white paper and the light absorbing characteristics of the black platen to determine when paper is installed in the printer. As the printer becomes older, the platen tends to take on a shiny (reflective) appearance from the build up of ink and paper deposits. Over time, this can reflect enough light to tell the the paper-out sensor that paper is in place when in fact there is no paper in the printer.