DMXZone DW CS6 extension problem

I can't instal the Dreamweaver CS6 extension xdmxHTML5 slide show, from DMXZone. The Adobe Extension manager CS6 returns an error "Impossible to update the menu". I'm running a Mac Pro machine with Mac OS X 10.9.1. Any hint?

I've cleared the DW cache as explained here http://www.dmxzone.com/go/16740/clearing-dreamweaver-s-cache/  w/o any luck.

Further details:

OS X in Italian

Extension manager version 6.0.8.28

dmxHTML5 Slide show v1.5.0

Dreamweaver CS6 V12.0 build 5861 Italian (installed over a german version)