Why is there a question mark over a printer icon on my dock?

I have just installed a new printer on my computer. I also have another printer installed along with this one. I put this new printer's icon on my dock. Now my old printer icon is showing a question mark over it. I set my new printer to be the default printer. Didn't know if that was the problem, so reset the default printer to be my old printer, but icon stayed. Reset new printer to default and then turned on the old printer. Question mark still there. Set old printer to default and tuned on the old printer. Set old printer to scan to see if setting it up to use it would do something. Question mark still there. I am stumped. Anyone know why this is happening? It just bugs me that it won't go away.