Canon MX870 Series User Manual page 943

The card is currently writable from PC.
Set to [Not writable from PC].
and then turn on the machine. If the same error occurs,
contact the service center.
The Card Slot is set to Writable from USB PC or Writable
from LAN PC.
You cannot print from the memory card or save the scanned
data to the memory card when the Card Slot is set to
Writable from USB PC or Writable from LAN PC. After writing
on the memory card, set to Not writable from PC again.
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