In fact, you need to set up your site so that it automatically rewrites to one or the other -- either have the www or not, but don't allow users to use both.
About my Battle.net login issue, it would be a problem the fact that I use PHP 5.3? That's strange, but most of external account works, Tumblr too, but just Battle.net having this weird issue...
It redirect fine to Battle.net login form then when I hit connect it redirect to the forum page that says "An unexpected error occurred. Please try again later."
Alright I've been out of the country for a few weeks so I'm sorry.
I will be releasing an update fixing a few issues on Friday. The addon isn't abandoned it's just been one crazy holiday haha!
I will also add a setting to enable errors so i can get more information sent to me to help debugging.