Hi John, the machine keeps asking you to clean the corona wire because on start up or especialy when the machine readies it's self to start printing, it passes a voltage through the corona wire which helps the drum erase the charge on the organic photo compound the drum is covered in.
If the machine sees any problem with the transfer of this voltage it thinks there is a problem.
The corona wire can be cleaned by sliding the blue tab on the top of the drum from right to left a few times.
You should check to see if this wire is broken ..it a very thin wire about the thickness of a human hair, if the wire is not broken then try cleaning the thin metal grid below the corona wire with a cotton bud , being carefull not to break the wire.
If this doesnt work then it sounds like the high voltage connection on the drum is faulty, and you will need to purchase a new drum ( or take it back to the supplier and say it is faulty and you want it replaced).
You ould also clean the surface of the drum itself carefully with a soft DRY clean cloth.
The only other cause is the high voltage supply pcb is faulty. Which if the machine is out of warranty is prohibitavely expensive to repair.

Hope this helps