Error

CUSTOM CODE:

Function CheckSignificantDate(i as integer) as Integer
Dim msg as String

     msg = ""
     If ( i = 15  )  Then
 msg=" Date Diff should be  more than 15 Days"
     End If

     If msg <> "" Then
 MsgBox(msg, 16, "Report Validation")
 Err.Raise(6,Report)                    'Raise an overflow
     End If
End Function

EXPRESSION:

=CODE.CheckSignificantDate(DateDiff(DateInterval.Day,Parameters!ToDate.Value,Parameters!FromDate.Value,))

                     Here I am facing one more problem.In custom code if I take condition (i < 15), for each value script is raising.(i.e for every number.ex: 1,24,33,67..... )