popover doesn't open pop over

Hi,

I’ve installed the plugin pop over on WordPress Version 3.3.1 but it doesn’t work.

Only the following plugins are installed and active:

– E-Newsletter

– WordPress Importer

– WPMU DEV Update Notifications

– Popover plugin

– Test Head Footer (this plugin did install together with “Popover plugin”. When I deactivate, then Popover plugin gets deleted.)

Template installed:

WPMU Nelo 2.2.5

Domain:

http://www.dateornext.de

I receive the following warning in the backend.

Your active theme: Has the call to <?php wp_head(); ?> but it is not called directly before </head>

Cheers, Oliver