We purchased a 400 and hooked it up yesterday. This is with a Mac running Snow Leopard (OS 10.6.8).
Nothing. All attempts to get it to print showed just a General Print Error which was not helpful.
I erased all software installed from the installation disc. Downloaded new software from their site. Installed that.
Still did not work.
Searching for answers I found that Dymo’s “global” site was far more helpful than their U.S. site which I found quite odd. Secondly, I found an answer that helped.
A user-board poster said to unplug the printer after the software installation. Then plug it back in. I unplugged both power and the USB cable. Waited a few seconds. Plugged them back in.
Suddenly, I could print from the Dymo software.
Still could not print with this plug-in. I shut down the computer.
Today, turned on the Mac, opened Safari, logged into our web site, selected “Print Shipping Label” and it immediately worked.