Building an old PC - trouble with A8N32-SLI Deluxe

I'm trying to put together a system using an A8N32-SLI Deluxe. When it boots up, I get a message saying "chassis intruded! fatal error. system halted." I didn't find anything in the BIOS to turn that off. The jumper on the MB is set to the default setting. I even repalced the jumper thinking it might not be making good contact between the pins. Any ideas what could possibly fix this problem?