User response() function in SAP WEBi

Hi Experts,

I have created a Formula variable in Bex with name "Exchange Rate" which is ready for input and its type is Number.

when i Created Webi report over this, I get the prompt with Exchange rate.

Now, My requirement is to show the Total value = Stock  * unit cost * Exchange rate if user put some vaalue in Exchange rate prompt say 2.3.

If user doesn't put anything in Exchange rate Prompt(means left blank) then Total Value = Stock * unit Cost.

I used the userresponse function on the exchange rate but it wont work. I am getting #error in the column.

First i Create a variable with name Exchg Rate = userresponse("[Exchange rate]")

and then i created the variable Total value =If(IsNull([Exchg Rate])) Then Stock * unit Cost ELSE ( Stock  * unit cost * Exchange rate).

But i am not getting the desired results.

Please advise/help on this.

Thanks,

Abhimanyu Sharma