hello I'm trying to generate crystal report based on the two dates selected by the user ...

the selection formula editor gives me the error "a string is required" when I want
to save and close my formula , can any1 help me whts wrong with my formula shown below ,

{records.entrance_date} >= {?entrance_date} and {records.entrance_date} <= {?entrance_date2}

both ?entrance_date and ?entrance_date2 are of date data type



thanks