I have my MP (with 3 internal drives) connected to an APC 1200 and I have to wait for the UPS to go through its startup cycle (battery test etc) so that the green light is steady before I hit the start button on the MP. If I don't then the USP gives me an Overload warning. I'm sure this is due to the fact that I have my HP Laserjet, DSL Modem, and a Netgear wireless router hooked up to the "always on" outlet of the UPS, and when the UPS powers up it also powers my USB hub and DROBO external TM with 2 discs. These loads may push the UPS over the top when the MP starts up (and presumably draws maximum load).