I have the old freebie (HP C4280). It's plugged into a USB hub. It doesn't work unless I unplug the USB cable, then plug it back in. Then it works fine. I haven't determined the exact amount of time that has to pass to make it stop working, but it's not long. I don't think it's the USB hub. I'm on my second one. Both were high-end (expensive) powered hubs. Same issue with both, yet all my other devices always work fine. Is this more likely to be an issue with my computer (Mac Pro) or the printer?