Output parameter issue in sql server and c#

Question

Why if I have this stored procedure created with an output parameter, I'm getting the following error:

sp_DTS_InsertLSRBatch expects parameter @ErrorMsg which was not supplied

Stored procedure code:

set ANSI_NULLS ON
set QUOTED_IDENTIFIER ON
go


ALTER PROCEDURE [dbo].[sp_DTS_InsertLSRBatch]  
    @LSRNbr varchar(10),
    @BatchNbr varchar(10),
    @ErrorMsg varchar(20) output
AS
BEGIN   
    SET NOCOUNT ON;    

    if not exists(select *
                from tblDTS_LSRBatch (nolock) 
                where LSRNbr=@LSRNbr and BatchNbr=@BatchNbr)
    begin   
        -- check if BatchNbr exists under another LSR
        -- if not add (LSR, BatchNbr) else error

        if not exists(select *
                from tblDTS_LSRBatch (nolock) 
                where BatchNbr=@BatchNbr)   

            insert into tblDTS_LSRBatch (LSRNbr,BatchNbr) values (@LSRNbr, @BatchNbr)       
        else    
            set @ErrorMsg = 'Batch dif LSR'     
    end
END

C# code:

SqlConnection conn = new SqlConnection(ConnStr);

try
{
   conn.Open();                

   for (int i = 0; i <= lbxBatch.Items.Count - 1; i++)
   {
       SqlCommand cmd = new SqlCommand("sp_DTS_InsertLSRBatch", conn);
       cmd.Parameters.Add(new SqlParameter("@LSRNbr", txtLSR.Text));
       cmd.Parameters.Add(new SqlParameter("@BatchNbr", lbxBatch.Items[i].ToString()));
       //Output parameter "ErrorMsg"
       SqlParameter pErrorMsg = new SqlParameter("@ErrorMsg", SqlDbType.VarChar, 20);
       pErrorMsg.Direction = ParameterDirection.Output;

       cmd.CommandType = CommandType.StoredProcedure;
       cmd.ExecuteNonQuery();  <--- ERROR

Answer 1

In your code you haven't added the pErrorMsg parameter. Add this line:

cmd.Parameters.Add(pErrorMsg);