在.NET程序集中向ADODB命令添加参数时出错

With ADODBCmd 
.ActiveConnection = ADODBConn
.Prepared = True
.CommandType = CommandTypeEnum.adCmdStoredProc
.NamedParameters = True
.CommandText = Sql_GetMyBook   
.Parameters.Append(.CreateParameter("@book",DataTypeEnum.adChar,ParameterDirectionEnum.adParamInput,50,MyBook))
End With

我得到一个投射错误……

System.Exception was unhandled
Message=System.InvalidCastException:
Unable to cast COM object of type
‘System.__ComObject’ to class type
‘ADODB.InternalParameter’. Instances
of types that represent COM components
cannot be cast to types that do not
represent COM components; however they
can be cast to interfaces as long as
the underlying COM component supports
QueryInterface calls for the IID of
the interface.

在线：

.Parameters.Append(.CreateParameter("@book",MyBook))

有任何想法吗？

存储过程：

ALTER PROCEDURE [dbo].[GetMybook]
    -- Add the parameters for the stored procedure here
    @book char(50)
AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    -- Insert statements for procedure here
    SELECT BookTitle,Author,PulishedDate
    FROM        Library
    WHERE       BookTitle=@book