Inaccurate error message

After reading the suggestions here, I tried cleaning the contacts of the cartridge with a Q-tip cotton swab, SLIGHTLY dampened with rubbing alcohol. This seemed to pretty much stop the problem, though it did re-occur occasionally throughout the life of that cartridge. Once I replaced that cartridge, it has never happened again. I guess this shows that you can (rarely) get a cartridge with bad contacts. If this ever happens again, I would return the cartridge to the retailer and get a new one.

P.s. PS Dave: ur a jacka$$ :(

According to Canon's website:

Details Print Friendly Version Issue: ERROR LCD: More than one ink tank of the following color is installed U071
Solution: Replace defective ink tank (MP500 / MP800)

Replacing An Ink Tank Use the following procedure to replace empty ink tanks or when an ink tank error appears.

1. Confirm that the printer is powered on and press the <Open> button. (The paper output tray will open.).
   
   
   
   
2. Lift the scanning unit (printer cover) completely. (The print head will move to the replacement position.)
   
   
   
   Note: When the scanning unit (printer cover) is opened more than ten minutes, the print head moves to the right side. If this occurs, close the scanning unit (printer cover), and open it again.
   
   
3. Open the inner cover.
   
   
4. Press the ink tank's tab (1), then remove it from the slot (2).
   
   
5. Unpack the ink tank and pull the orange tape off completely in the direction of the arrow andinaccurate error message - 05sj00141_05_en.jpgr />
   
   
   Note: Tear the orange tape carefully along the dotted line. If the orange tainaccurate error message - 05sj00141_06.jpgting problems may occur.
   
   
   
   
   <4> Tape is completely removed.
   
   <5> Tape remains. Remove the orange protective cap located on the bottom of the ink tank by twisting as shown in the diagram.
   
   Caution: Do not touch the ink tank contact <6>. Doing so may cause printing problems. Do not squeeze the side of ink tanks as this may cause the ink to leak out. Do not reattach the protective cap once you have removed it.
   
   
6. Insert ink tanks into the print head.
   
   Note: Press the inaccurate error message - 05sj00141_08_en.gifn the ink tank firmly until you hear a click.
   
   
   
   
   
7. 
   
   
   <7> The ink tanks are installed properly.
   
   <8> The ink tanks are not installed properly.
   
   
   Note: Click for Ink Tank Lamp indications.
   
   
8. Close the inner cover and the scanning unit (printer cover).
   
   Caution: When closing the scanning unit (printer cover), be careful not to jam fingers.
   
   Note: The next printing begins, the print head cleaning will begin automatically.
   
   

• On: The printer is ready to print.
  
• Slow flashing (at about three second interval): Ink is low. Prepare a new ink tank.
  
• Fast flashing (at about one second interval): Ink tank is empty, or the printer is not ready due to an error.
  
• Off: An error has occurred and the printer is not ready to print.

I am having the same problem. I found a few other forums on this issue that suggest cleaning the contacts on the cartridge. Opening the cover and reseating the cartridge only worked the first few times for me and now even cleaning the cartridge fails. Only other thing is to replace the cartridge all together I guess.