CMS Impossible to configure widgets
 

In CMS / Widget (admincp) when I click on "configure" nothing happens. A popup window is supposed to show up (it does in a test forum), but not on my live site.
I re-uploaded all files again but without any success.
Anything I can check?

I precise that there was only one widget on that page. I added another one from the drop down list but I can't change the settings.