I'm getting this all the time now with my Brother laser printer.
It solved by taking out it's usb cord and then reinserting it.
Anyone know what this means or how to solve it? thanks.

As I see it, either the USB port is bad or the cable is bad. Try a different USB cable and see if that helps. If the cable is not responsible, try a different port.

thanks J. ok, very long cable, do I hope I have a spare to try.
The port, darn, just bought a new one. But I'll test that idea if the new cable does not solve it.

If the iMac is new, you should be covered under warranty if the port is bad. The cable length might be an issue. Try a shorter cable if possible.

Jon makes an important point: you didn't say how long your printer cable is, but if it's over 16 feet (and quite possibly already over 10 feet), and doesn't include a USB bridge you're likely to have problems. See the USB FAQ for details.

As Jon has already mentioned cables, ports, and hubs are logical places to start looking. To elaborate on what alternaut said, the quality of a USB cable and the connectors can be critical, and the longer the cable the greater the impact of quality. (Anticipating the question, "How do you tell the qualiity of a USB cable? my answwer is you get what you pay for.) Other USB devices daisy chained with the printer can also cause miseries.

Third party software such as drivers for a USB mouse can cause USB devices to mysteriously go offline, especially it seems when the computer goes to sleep. Check System Preferences for Other preference panes and Accounts > Login items to see if anything even remotely associated with the USB or USB devices are in there.

Thanks guys,
Actually this is a very long usb cable. The printer is the farthest distance than any other peripheral from the computer.

The cable was quite old, so I'm hoping that it. So far (only couple of days, the new cable is not getting the offline error -- will keep you posted if that changes.)

It's going to a hub, new hub.

Ok, tested new long cord, and a different hub and still get printer is offline...

Eliminating the hub from the mix, i.e. connecting the printer cable directly to a USB port, would be more telling.

Since you haven't responded to my suggestion to eliminate the hub from the mix, I'll guess that your issue has perhaps been resolved.

Would you please fill us all in on the details of if and how that happened?