Super Micro P6DGS

I’m using a Super Micro P6dgs motherboard. It currently has 256mb of ram. The board consist of 4 memory banks with 128mb in the first two slots.
I am upgrading to 1 gb of ram by using a 1 gb pc100 sdram module. When trying to install the new ram i get memory errors. I’ve tried to install the 1 gb module with the other two and still no luck. I’ve also flashed the bios from the orginal version of 2.2 to 3.1 and still getting the same error. The board is capable of holding 2gb of ram.

Does anyone have an idea of what could be the problem?