That system used a rolling BIOS meaning it contains 2 complete copies of BIOS incase one somehow gets corrupted.
Sounds like your secondary BIOS page is corrupt.
You may want to try re-flashing the BIOS. http://downloadcenter.intel.com/Detail_Desc.aspx?agr=Y&DwnldID=11857&lang=eng
If it is a random bit error, that should fix it.