Not my problem (anymore!), just a solution in case someone else wandering through the forums has this issue.
Scenario: a Mac connected to the Internet wirelessly is also attempting to use a printer that is wirelessly connected to the same network.
Problem: the printer's utility says the printer is not connected to the network, but you know it is and the printer's settings show that it is.
Solution: many in-home or small business set-ups actually have many "networks in the same network". That is, there could be a 2.4 GHz, 5 GHz and a guest network. The printer is on only one of these, and the device that is attempting to print must be on the same network, if the device is wirelessly connected to the Internet. If the device is connected by Ethernet cable, this problem does not occur. Technically speaking the device and printer must be using the exact same SSID.
Example: Printer is wireless on MyHome 2.4. Your new iMac Air is using MyHome 5. Printing won't happen. Switch the iMac to MyHome 2.4 and all is well.
Comment: Many home network setups may not show the "2.4", which is often the default, but the additional 5 GHz network will show something to distinguish it, possibly even a different name. The same is true of the network names if you use a router relay.
