Dumb XY3+ question

[rrr@xxxxxxxx (Yo Intl.)]

I wanted to define Ctrl+Shift+B as "dir *.bak" (no urgent need,
but it seemed like a good idea), but when I insert the line
48=BC,d,i,r, ,*,.,b,a,k into the keyboard file at the needed location,
nothing happens. The computer just pretends there is no definition.
All other key definitions work. Any particular reason for this? Did
I stumble upon another built-in DOS limitation? Tia

--Rene von Rentzell, Tokyo 
--"I did not inhale." "These allegations are false." "My statements
--were legally accurate". "It depends on the meaning of 'is'".
--"Earlier today I ordered a military strike".