AMD 761/VIA Pro266chipsets support 200266MHz SDRAM because it uses Double Data Rate to do transferring. It runs at the speed of 100133MHz externally between the SDRAM and the NorthBridge, while the SDRAM itself runs 200266MHz internally. Thus, 100MHz means the transferring rate between the SDRAM and the NorthBridge.
Please ignore this error message and continue flashing. Or you can use quick update BIOS mode, for example, type "Awdflash 6BX.F1d /sn /py /cc /r", and then press [Enter] key.