Type Library的错误

在Type Library Editor中写
  IArcFeatureLayer = interface(IArcLayer)
    ['{39257EB2-75F9-4F2F-B96D-158987A5FD97}']
    function AddGeometry(AGeometry: OleVariant): OleVariant; safecall;
    procedure DeleteFeatures(AFeatureCursor: OleVariant); safecall;
    procedure DeleteSelectedFeatures; safecall;
    function GetSelectedFeatures: OleVariant; safecall;
    function Get_Property1: Integer; safecall;
    property Property1: Integer read Get_Property1;
  end
保存时提示“继承等级中有重复的ID”。这个很令我奇怪，接口是可以继承的，怎么在这里还不让呢？