AdDate Parameter To Stored Proc.

I am trying to pass a VBScript Date variable as value to an ADO adDate
parameter of a stored procedure (which runs in an SQL Server).
If I add the parameter like this:

oCmd.Parameters.Append oCmd.CreateParameter( "@p_Date", adDate,
adParamInput, , dParam)

where oCmd is of type ADODB.Command and dParam is a VBScript variable of
type Date
then when trying to execute the stored procedure I get the following error:

Optional feature not implemented

I was able to get round this by passing a string value in an adVarChar
parameter, but it would be easier and more readable with adDate and
Date-type variables. Is this latter possible?