Near the microswitches inside the LaserWriter, there is a bracket held in
place by two screws (but no lock washers). As old toner cartridges are
removed and new ones installed, these screws and the bracket become loose.
This causes the toner cartridge to 'disappear to the LaserWriter' as the
drive train tightens to pull the paper through, causing the LaserWriter to
stop printing.
When printing stops, the tension in the drive train slackens and the toner
cartridge 're-appears'. This series of events results in what appears to
be a paper jam. At first, this can happen about once a week. Then it begins
to happen every day. Eventually, the bracket becomes so loose that the
cartridge 'disappears' entirely.
To fix the problem, just adjust the bracket and tighten the screws.