Windows refuses to believe printer is online unless I delete and re-add it

I have a Canon MP560. It is online, in the sense that

1. I can connect to its internal web server.
2. If I delete and reinstall it, Windows (Windows 7) will then recognize it.

In all other cases, neither my PC nor my Mac (purchased last week, running whatever is the latest and greatest Mac OS) recognizes that the printer is online.

The printer is statically configured to use the same IP address, so that's not an issue.

Because the printer works just fine with Windows after delete and re-add, I assume that the issue with the Mac is that I haven't installed whatever drivers Macs need to talk to Canon printers over a network.

For the windows PC, check that SNMP status polling is configured correctly, or disabled, on the Windows printer port. I've seen this cause issues on printers that don't implement SNMP properly, which is normally used to monitor network printers to see if they are online or offline.

To check this, you need to check the configuration of the the "port". Windows communicates with network-attached printers using "ports" - which is a legacy from way back when you could only connect printers directly to computers, using physical serial or LPT ports. For each network-attached printer, you will have a printer port pointing to the IP address of the printer.

You can see the printer ports on the system by:

1. Click Start, and then click Devices and Printers
2. Right-click the printer, and then click Printer Properties
3. Click the Ports tab.

This will show all printer ports on the system. Find and select the port for the MP560, it will have a tick/check next to it, and should be named IP_

1. Click Configure Port...
2. Click to clear the SNMP Status Enabled check box, click OK, and then click Close.

For the Mac, I would make sure you install the drivers for the printer from Canon. Quite often OSX will pick a printer up, but won't be able to communicate with it, or use some of the advanced features of the printer (such as ink level monitoring) until you've got the right vendor drivers installed. Try the latest ones from the Canon website for this model. Consider grabbing a copy of the scanning and wireless setup utilities from the same page.

Is the printer configured to "go to sleep" at all? I've had devices that would do this and NOTHING would get them back but a hard restart. I know that's slightly different from your situation, but I would look into it. If it does it may be in a twilight state.