Wordpress 3.9.1 + WampServer Installation

Hello Community, I have a little (but annoying) problem with my current Wordpress project. I work local on a WampServer installation and have no problems since today.
I installed the newest wordpress Installation 3.9.1 and try to install a theme and/or the woocommerce plugin. With both attempts, I got the error (sorry in German) "Bist du sicher, dass du das tun möchtest? Bitte noch mal versuchen." I think in the englisch wordpress version you get the error "Are you sure you want to do this please try again". I think it is a WampServer installation problem, because i try the same with a XAMPP-Server installation and all works fine. At first i thought the problem is the maximum allowed size for uploaded files in the php.ini. But I got the same error with an increase to 40MB. I just installed Wordpress with no other updates of the plugins, so I think I can't install wordpress cleaner. Does anyone has an idea to fix the problem, or any tips?

Thank you very much.
Cya Arnim