Canon PIXMA MP450

I had the same problem and spoke to canon australia technician. Any 4 number code means it is a servicable error. 6500 code specifically says take to a service centre...
bugger....but thats what they told me...

An Error Message Is Displayed On The LCD If an error message is displayed on the LCD, take the corresponding countermeasure described below.


Message
Action
There are no photos in memory card.
There are only invalid images on the memory card.
Photo data edited/processed on a computer should be printed from the computer, not from the camera.
There is no paper.
Reload the paper correctly and press [OK].
The paper is jammed.
If paper has jammed in the machine, clear the jam, reload the paper in the machine correctly and then press [OK].
Ink has run out.
U041
Replace the FINE Cartridge, and close the Scanning Unit.
If printing is not finished yet, just press [OK] on the machine to continue printing in the "no ink" state.
Replace the FINE Cartridge with a new one as soon as possible after printing finishes. The machine may be damaged if printing is continued under the ink out condition.
The following ink cartridge cannot be recognized.
U051
U052
U053
U059
The FINE Cartridge may not be installed properly, or the Cartridge may not be the compatible with this machine. Install the appropriate FINE Cartridge. If lines are misaligned or the resulting output is not satisfactory, carry out the FINE Cartridge Alignment.
Some ink cartridges are not installed in place.
U075
U076
Confirm that the FINE Cartridges are installed in the appropriate positions.
The ink absorber is almost full. Press [OK] to continue printing. Contact the service center.
The ink absorber is almost full. Printing will no longer be possible once the ink absorber is full. Contact the service center immediately. Press [OK] to continue printing.
Incompatible device detected.
Depending on the model or brand of your device, you may have to select a print mode compliant with PictBridge before connecting the device.
You may also have to turn ON the device or select Play mode manually after connecting the device to the machine. Perform the necessary operations according to the instruction manual supplied with your device.
If the error is still unresolved, there is a possibility that you are using a digital camera or digital video camcorder that is not supported by this machine. Use a digital cameras or digital video camcorder compatible with this machine.
Auto head align has failed.
Make sure all required boxes on the head alignment sheet are filled in, and that the sheet is set in the correct position and orientation on the Platen Glass.
If the machine is connected to the computer, you can align the FINE Cartridge using the MP Driver. Follow the procedures described in the Printer Driver Guide.
The following ink may have run out.
U162
This FINE Cartridge may have previously been used, or the ink may have run out. The function for detecting the remaining ink level will be disabled since the remaining ink level cannot be correctly detected. If you want to continue printing without this function, press [OK]. Canon recommends to use new genuine Canon Cartridges in order to obtain optimum qualities.
The following ink cartridge cannot be recognized.
U140
The FINE Cartridge may not be the compatible with this machine. Install the appropriate FINE Cartridge. If lines are misaligned or the resulting output is not satisfactory, carry out the FINE Cartridge Alignment.
Printer error.
An error requiring servicing might have occurred. Turn OFF the machine, and unplug the power cord of the machine from the power supply. After a while, plug the power cord of the machine back in and turn ON the machine. If the same error occurs, contact a Canon service representative.