Communication error has occurred - Canon PIXMA printer

This was driving me nuts! I tried many of the other ideas offered in these discussions, but nothing worked. Sometimes my Canon PIXMA MP640 WiFi printer would work, usually it wouldn't. I would get "A communication error has occurred" message on my MacBook Pro (Snow Leopard) and the print job would just stay in the queue until I deleted it. Most of the time I needed to re-enter the network password at the printer BEFORE EVERY PRINT JOB which was a pain because the password was 10 characters long and I could only dial in each letter one at a time.

If you are having similar trouble, before you do anything CHECK THE WIFI SIGNAL STRENGTH USING THE PRINTER MENUS! On my model, this was done by going from the Home menu to Settings->Device Settings->LAN Settings->Confirm LAN settings->Print LAN Details. If the signal strength on the printout shows less than 50%, there is too much interference from other electronics in the area (or the printer is too far from the router). In my case, the printer was in the next room, i.e., not too far from the router so I knew it had to be EM interference.

At first, my signal strength was showing 36%. Then I moved the printer into the same room as the wifi router, within 7ft and directly in line of sight of it and it went to 62%. I thought it should be much higher, so I moved the printer to within 4ft and it went to 80%. Then I unplugged the LCD TV (which was NOT turned on at any time) that was on the counter nearby, and it jumped to 90%.

After months of poking at this problem and finally resigning to the idea that the printer was broken, I tried this and now it works perfectly as long as the TV is unplugged. I plan on moving the router away from the TV so I won't have to unplug it whenever I print.

Hope this helps!