I have a Canon PIXMA MX340 and when I try to print sometimes it gives me an error saying "Support Code : 300 The printer does not respond. Make sure that the printer is plugged in, powered-on, and properly connected to your computer." and I know the printer is on and connected to Wi-Fi because the other Windows computer has never had this problem and instantly sends the request and the printer receives it almost instantly as well. Also when I try to scan I go to the printer and I hit "Scan" and it asks you to select the computer so I do and then I hit color and it says please wait a while and in a few minutes it just goes back to the original screen and doesn't scan. Meanwhile the Windows computer works fine (sometimes). Before, all this stuff used to work. Can anyone help me?
If it's working fine with your other computers over the same network, sounds like a possible driver issue. Here's a link to the drivers for the model printer you stated in your post.
Also, at the end of your post, you said, "Before, all this stuff used to work." Before what? Did something change?