Are you sure that the current position is already within the "standard" element? Maybe just try it from the document root: //Nozzle-Flange-Weight/Standard/...
At the link below you can download cooktop. This is a nice freeware tool that ain't perfect, but very handy. You give your xml and xpath and with one button click it will produce the result or give the error. Very nice for writing and checking xpath.
http://www.tucows.com/preview/350904[
^]
Good luck!