I have a Canon PIXMA MP500. I have refilled my own cartridges for months and have not experienced any problem. Recently my printer will not print and gives message "two cartridges or same color". Not true. Now and then I hold down the "stop/reset" button for 5 seconds and it goes on to print. I am getting this message almost every time I try to print. Is there an override code or procedure I can use that will allow my ink cartridges to be recognized? I need help bad. Thanks for your ideas.