FSB -> Front Side Bus. As lsd obliquely says, it's the speed at which the processor communicates with memory chips. Can't download the manual (site sucks) but their FAQ suggests you put memory modules in from DIMM 3 to DIMM 1. I think the 3 is the one farthest from the processor. Maybe the other way around... Anyway, try changing the slot into which you put the module. That's all I can think of.

-- erlik