DataSet’ is a ‘namespace’ but is used like a ‘type’

Error 1 'AdvoDiary.DataSet' is a 'namespace' but is used like a 'type' D:\AdvoDiary\AdvoDiary\ReportViewer\rptBilling.cs 25 9 AdvoDiary

namespace AdvoDiary.ReportViewer

public partial class rptBilling : Form


    Common sCom;
    DBHelper myDB;
    string sOLE;
    clsGlobalVar objGlob;
    OleDbConnection cn;
    OleDbDataAdapter sDA;
    DataSet sDS;
    OleDbCommand cmd;