I seem to remember my A7N8X giving me that message way back when(OK, December at least) I had my XP2400 in it. I think that it gave that message when I tried to drop the multi back below 13 without disabling the high bit sense bridge.

Walter E. Kurtz, were you by any chance trying to lower the multiplier beolw 13 without doing the bridge trick to your 2100, assuming that it is a Tbred B 2100? If so, then leave your multi at 13 and overclock the fsb speed.