Can't get the API to work…

I get this error in the log:

Last Error detected

Last Error: 2016-01-05 19:44:57: exception 'Google_IO_Exception' with message 'HTTP Error: Unable to connect: 'fopen(https://accounts.google.com/o/oauth2/token) [<a href='https://de.php.net/function.fopen'>function.fopen</a>]: failed to open stream: no suitable wrapper could be found'' in /users/bestunder/www/wordpress/wp-content/plugins/google-analytics-dashboard-for-wp/tools/src/Google/IO/Stream.php:106
Stack trace:
#0 /users/bestunder/www/wordpress/wp-content/plugins/google-analytics-dashboard-for-wp/tools/src/Google/IO/Abstract.php(135): Google_IO_Stream->executeRequest(Object(Google_Http_Request))
#1 /users/bestunder/www/wordpress/wp-content/plugins/google-analytics-dashboard-for-wp/tools/src/Google/Auth/OAuth2.php(113): Google_IO_Abstract->makeRequest(Object(Google_Http_Request))
#2 /users/bestunder/www/wordpress/wp-content/plugins/google-analytics-dashboard-for-wp/tools/src/Google/Client.php(133): Google_Auth_OAuth2->authenticate('4/_F7AnKQ4Z0PGR...')
#3 /users/bestunder/www/wordpress/wp-content/plugins/google-analytics-dashboard-for-wp/admin/settings.php(739): Google_Client->authenticate('4/_F7AnKQ4Z0PGR...')
#4 [internal function]: GADWP_Settings::general_settings('')
#5 /users/bestunder/www/wordpress/wp-includes/plugin.php(525): call_user_func_array(Array, Array)
#6 /users/bestunder/www/wordpress/wp-admin/admin.php(236): do_action('toplevel_page_g...')
#7 {main}

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