=SUM(--if(ISNUMBER(B6:K300);ABS(B6:K300)<100))
This is an array formula therefore should be netered with CTRL+SHIFT
+ENTER

Pedro J.

I see why you did it now (I must admit to wondering about that), but I would
use ISNUMBER, then it simply becomes

=SUM(IF(ISNUMBER(B6:C9),IF(ABS(B6:C9)<100,1)))

the intent is nice and clear then.