isnull on date type doesnot return records although exist

Hi All,

       In my report i pass on the parameters start date and end date. I want the result set to include the records whose end date is null. I have explicitly used the isnull function in Record Selection Formula Editor but it does not bring up any records although they exist. If i run the same query in SQL i get result set which has End Date as Null i read in some forums that isnull should be first function in Record Selection which I did i have got other conditions and it does not retain this even though i placed it first. Any suggestions how this can be fixed ? Am on crystal reports version 10.0.5.1506.

Thanks,

Prathima