C#

private void btnSearch_Click(object sender, EventArgs e){
            
            string connectionString = "Data Source="" I verified correct conn String, it works ";
            string  commandText = "sp_Case_Search";

            using (SqlConnection conn = new SqlConnection(connectionString))
            {
                SqlCommand cmd = new SqlCommand(commandText, conn);
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.CommandTimeout = 600;
                
                conn.Open();
 cmd.Parameters.Add(new SqlParameter("@Field", SqlDbType.VarChar));

                cmd.Parameters.Add(new SqlParameter("@Field", SqlDbType.VarChar, 50));
                cmd.Parameters.Add(new SqlParameter("@Search", SqlDbType.VarChar, 500));
                
                //add input parameter from stored proc and set value
                
                /*DateTime edtPicker = Convert.ToDateTime(EnterdateDateTimePicker.Value);
                DateTime udtPicker = Convert.ToDateTime(UpdateDateDateTimePicker.Value);
                
                cmd.Parameters.Add(new SqlParameter("@ID", SqlDbType.Bigint));
                cmd.Parameters.Add(new SqlParameter("@EnterDate", SqlDbType.DateTime)).Value = edtPicker;
                cmd.Parameters.Add(new SqlParameter("@EnterTime", SqlDbType.VarChar)).Value = EnterTimeTextBox.Text;
                cmd.Parameters.Add(new SqlParameter("@EnterBy", SqlDbType.VarChar)).Value = EnterByTextBox.Text;
                cmd.Parameters.Add(new SqlParameter("@CaseTypeID", SqlDbType.Int));
                cmd.Parameters.Add(new SqlParameter("@MethodTypeID", SqlDbType.Int));
                cmd.Parameters.Add(new SqlParameter("@UpdateDate", SqlDbType.DateTime)).Value = udtPicker;
                cmd.Parameters.Add(new SqlParameter("@UpdateBy", SqlDbType.VarChar)).Value = UpdateByTextBox.Text;
                cmd.Parameters.Add(new SqlParameter("@CaseDocNumber", SqlDbType.VarChar)).Value = CaseDocNumberRichTextBox.Text;
                cmd.Parameters.Add(new SqlParameter("@SenderAddress", SqlDbType.VarChar)).Value = senderAddressRichTextBox.Text; */
                
                cmd.ExecuteNonQuery();
                
                cmd.Parameters.Clear();
                conn.Close();

            }

ALTER PROCEDURE [dbo].[sp_Case_Search] 
	-- Add the parameters for the stored procedure here
@Field varchar(50),
@Search varchar(500)

AS
BEGIN
	-- SET NOCOUNT ON added to prevent extra result sets from
	-- interfering with SELECT statements.
	SET NOCOUNT ON;

    -- Insert statements for procedure here
    declare @Criteria varchar(502) = '%'+ @Search + '%'
	SELECT 
	   [ID]
      ,[EnterDate]
      ,[EnterTime]
      ,[EnterBy]
      ,[CaseTypeID]
      ,[MethodTypeID]
      ,[UpdateDate]
      ,[UpdateBy]
      ,[CaseDocNumber]
      ,[SenderAddress]
            
    FROM  tblNewCaseEntry
        
    WHERE 
    CASE 
    When @Field = 'ServedBy' then ServedBy 
    When @Field = 'CaseDocNumber' then CaseDocNumber 
    When @Field = 'SenderAddress' then SenderAddress
    When @Field = 'Claim' then Claim 
    End like @Criteria
    ORDER BY EnterDate DESC;
END

using a1;
using a2;
namespace BasicLogic
{ class Form1:Form
   {
     ..
   }
...
}

File a1.cs
namespace a1
{...
}

File a2.cs 
namespace a2
{...
}