How to handle custom exceptions in ASP.NET C#, I tried following mechanism, but not executing.

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C#

ASP.NET

SQL

server

based on this following code i am going to get data from indent table by using stored procedure with two arguments (indno, incharge). so whenever the system exceptions ( like sql exception, Exception etc,.) occurred then i want to handle with custom exceptions like DAO catch block.. but not working.. i dont know where i did mistake.

Thanks in advance..

What I have tried:

public DataSet GetIndentsDetails(int indno,string Incharge)
        {
            DataSet DsIndentDetails = new DataSet();
            try
            {
                if (dbConn == null)
                    dbConn = CommonProcedures.GetConnection();
                dbCmd = dbConn.GetStoredProcCommand("usp_GetAllIndents");
                dbConn.AddInParameter(dbCmd, "IndentNo", DbType.Int32, indno);
                dbConn.AddInParameter(dbCmd, "Incharge", DbType.String, Incharge);
                DsIndentDetails = (DataSet)dbConn.ExecuteDataSet(dbCmd);                
                return DsIndentDetails;
            }
            catch (DBConnOpeningException dbConnOpenEx)
            {
                
                throw new DBConnOpeningException("Unable to Connect Database");
               // return DsIndentDetails;
            }
            catch(DBSelectFailedException dbSelExc)
            {
                throw new DBSelectFailedException("Select Statement Failed");
            }
            catch (DAOException DAOEx)
            {
                throw new DAOException("DAOException Occured");
                //return DsIndentDetails;
            }
            catch (IndentsListException ilistEx)
            {
                throw new IndentsListException("Could not load Indent List");
                //return DsIndentDetails;
            }
                       
            catch(ERPException erpEx)
            {
                throw new ERPException("ERPException Occured");
            }
            finally
            {
                dbConn = null;
            }
        }

Custom Exception
--------------------

public class ERPException : System.Exception
    {
        public ERPException():base()
        {
           
        }

 
        public ERPException(string arg1,System.Exception arg2):base( String.Format( "{0}",arg1), arg2 )
        {

        }
        public ERPException(string arg1): base (String.Format("{0}",arg1))
        {

        }
        //public ERPException(System.Exception arg1):base(arg1)
        //{

        //}
        
    }

public class DAOException : ERPException
   {
       public DAOException(): base()
       {

       }
       public DAOException(string arg1,System.Exception arg2):base(String.Format("{0}",arg1), arg2)
       {

       }
       public DAOException(string arg1):base(String.Format("{0}",arg1))
       {

       }
   }