Purge Data #error when UserResponse and ToDate function is used in same formula

Hi,

I have a formula which works well when there is data but when I purge the webi report I get #Error for the cells wherever I have used UserResponse and ToDate function in the same formula.

Ex: =FormatDate(ToDate(UserResponse("Enter Modified Date:");"M/dd/yyyy hh:mm:ss a");"MM/dd/yyyy")

I tired in multiple reports. I get the same error in all reports when i purge the data but when i unpurge and show the reports with data, I won't get any error.

Is this known issue? If anyone knows the solution. Please answer it.

(FYI, I am using BO4.0 SP5)

Thanks.