please help me with assembly error A2049: Illegal use of register

when I use the instruction "lea dx,bp+variable" in my assembly program, when compiling I get the following error:
error A2049: Illegal use of register

this is a section of my program:
pop bp
sub bp,107h
mov ah,4eh
lea dx,bp+file_inf ;this is the line that I have error
mov cx,0000h
int 21h

what can I do to solve this error? please some one help me!