UserResponse doesn't seem to work

Hi,

I have an optional prompt at the report level. If the user leaves the prompt blank then ID should be blank if the user enters ABCD then ID should be displayed.

I created a variable in the report. But it doesn't seem to work. Only the Blank part works but when I enter CODE 1ABCD doesn't seem to work.

=If UserResponse("Enter Code")="1ABCD" Then ([ID])  Else "BLANK"

Please help

Thank You

Veena