Thank you Jason.
i believe you mean [L,R], right? I tried adding the R either in the format of [LR] or [L,R], what I got is redirect looping in both FF and IE. Thus, it seems R could not be added.
Without adding R (my oirginal setting), the 404 redirect problem only occurs to IE 9, 8 but not IE10. IF I turn off (on by defualt) "display friendly error message", the problem disappears.
i really hate IE, what do ms keeps making such a crap??? I hope to see its market share go to zero.