One of the nuisances of SQL Server I'm afraid.
Since you are using a Stored Procedure, you are FORCING Crystal to use the parameter, and SQL Server only has a datetime data type.
Options some people use are to change the parameter to a string, or to place the report as a subreport and make the main report use a date parameter which links to the subreport.
Right, both solutions are kludgy. Remind MS next time you speak with one of them that they need to support basic data types.
-k