مشکل با Stored Procedure

[Babak-Aghili]

سلام.

متن کد و متن Stored Proc را نوشتم ام . خطایی که میگیره میگه : Invalid Cast Operation ....

CREATE PROCEDURE LoginProc

(@uId NVARCHAR(20), @uPass NVARCHAR(20), @uName NVARCHAR(20) OUTPUT)

AS

SET @uName =( SELECT @uName  FROM TblUsers WHERE 

(TblUsers.userId = @uId AND TblUsers.userpassword = @uPass))

GO

SqlCommand cmd= new SqlCommand();

			cmd.Connection = con;

			cmd.CommandText="LoginProc";

			cmd.CommandType = CommandType.StoredProcedure;			

			cmd.Parameters.Add("@uId",SqlDbType.NVarChar,20,"u  serId");

			cmd.Parameters.Add("@uPass",SqlDbType.NVarChar,20,  "userPassword");

			cmd.Parameters.Add("@uName",SqlDbType.NVarChar,20,  "userName");



			cmd.Parameters["@uId"].Value= textBox1.Text;

			cmd.Parameters["@uPass"].Value= textBox2.Text;

			cmd.Parameters["@uName"].Direction = ParameterDirection.Output;

			cmd.Parameters["@uName"].Value = "";



			con.Open();

			SqlDataReader reader= cmd.ExecuteReader();

			bool b = reader.Read();

			

			string name = (string) cmd.Parameters["@uName"].Value;

			MessageBox.Show(name);