Ditto that nunor. This means that your memory is capable of running at that speed but your system is not stable at that speed. I believe that the issue with running at that speed has to do with the bandwidth required. This will require tweaking NB voltage, GTLs, NB & CPU Skews, Pll, VTT, ect........Head spinning yet???

Take it easy and make small steps. If you're stable at FSB 400, then go to 410 and tweak that first and move up slowly one step at a time. As deachus has pointed out, it takes many hours of tweaking.