This information is directly from the Canon website, basically it suggests something is stuck inside. Other articles I found mentioned one person found a paperclip stopping the works.
---- quoting Canon ----
6000/P03 - Orange and green light blinking 3 times
A service error has occurred.
- Turn off the printer.
- Disconnect the power cable.
- Open the printer cover.
- Check for any orange protective tape or white polystyrene and remove if necessary.
- Check that there are no foreign objects in the printer (such as a paper clip) and remove if necessary.
- Close the cover.
- Reconnect and turn on.
If the above solution has not resolved your error, please contact your nearest Canon authorised service facility using the link at the top of the page.
----- end quote ---
Best wishes -
PIXMA Printer Error Codes and Error Messages