Canon PIXMA iP8750 - Manual (Page 336)

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Cause
Printable disc (BD/DVD/CD, etc.) is not set.
Action
When printing on printable discs, use the disc tray supplied with this printer ("L" is on the upper side).
Place a printable disc on the disc tray, attach the disc tray to the printer, then press the printer's RESUME/
CANCEL button.
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