-451 means Extension Manager can't find the product supported by this extension, i.e., DW CC 2014. Please confirm that DW CC 2014 is not shown in the product panel of Extension Manager.
DW CC 2014 is supported by Extension Manager CC 7.2 and higher version. Please update Extension Manager to 7.2.1 first.
If Extension Manager still can't recognize DW CC 2014 after update, please refer to Re: Why can't I see InDesign CC in my Extension Manager CC.