This error occurred on a long print run after 100-200 pages. The printer stopped mid print with the Attention light, Ready light, and Go lights all on indicating a service error.
If you turn your Oki C5300 printer on and get the following error message on the control panel display:
SERVICE CALL
020:FATAL ERROR
The firmware DIMM is faulty. This is quite a common fault with this printer and is easy to repair.