This is a long shot, but do you, or did you have a USB connected UPS system connected to the PC?  I don't remember if ME had the monitoring capability, but if the PC was set to sense alrams from the UPS and it was never disabled or uninstalled connecting some other USB device such as your new printer could cause it to think it's a shutdown alarm from the UPS.

The other part is correct.  When you connect a USB 2.0 device to a 1.1 port you will get that message.  2.0 devices are supposed to be backward compatible with 1.1 ports, just transfer data at a slower speed, however, I don't see any difference in actual use.  I have two USB connected printers, one is a 1.1 device and the other printer is a 2.0 device, my port (and external powered hub) are 2.0 and the time to print to either one is about the same.

Thanks very much for the suggestion. I've never had a UPS; in fact the only USB device I've ever plugged into the PC is a Kodak card reader. (I have windows XP, by the way, if that matters at all).