Its possible that its the board, not sure, I dont have much experience with that manufactorer.
I do know that the Epox 8rda has a northbridge voltage issue that prevented, some of the boards, from reaching 200 FSB. Maybe there is a similiar issue with certian revsions of your board, may wanna do some research, find others that have used the same board you have and see what they say they can do.
I of course happened to get one of those Epox boards and was not happy at all. I had to buy a new board to get it past 200.
I also could be the memory, as mentioned before, you need a lil extra volts to get it to run at specs.
You could have a bad memory module that is causing the issue, how many modules are you using, have you tried them one at a time?
I find it odd that the board will let you up the FBS to 250 but you cant change the mem or CPU voltage settings. Not sure why you have that option if you cant up the dram or CPU voltages. Have you tried updating the bios? Some board do not run well with the factor bios version.