Just to get back on track here, there are a couple of alternatives to Poz Extender as well which you might want to look at if you can't get Poz Extender to work.
The Spread has Extender(i):
http://thespread.ghostoutpost.com/
Direct link to file:
http://thespread.ghostoutpost.com/ExtenderI.zip
Whilst you're exploring The Spread, it might also be worth having a look at some of their other plug-ins. Symmetry Tools has a version of Extender that works in Symmetry mode.
Pictrix also have ExtenderS
http://www.pictrix.jp/index2.html
All of these plug-ins are freeware. Hope that helps!