[Plugin: WorldTag] Plugin error

Hi,

I’m getting this error:
Warning: call_user_func_array() [function.call-user-func-array]: First argument is expected to be a valid callback, ‘register_wtsettings’ was given in /kunden/274177_67655/webseiten/wp-includes/plugin.php on line 405

Latest WP version installed.

http://wordpress.org/extend/plugins/worldtag/