White screen for new user

When I added a new user to the site, he was always getting a white screen after login.
WP debug mode revealed this error:

Fatal error: Uncaught Error: Cannot use string offset as an array in /usr/www/users/konopx/wp-content/plugins/only-tweet-like-share-and-google-1/tweet-like-plusone.php:552 Stack trace: #0 /usr/www/users/konopx/wp-includes/class-wp-hook.php(286): removeconflict('') #1 /usr/www/users/konopx/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters(NULL, Array) #2 /usr/www/users/konopx/wp-includes/plugin.php(453): WP_Hook->do_action(Array) #3 /usr/www/users/konopx/wp-admin/admin.php(156): do_action('admin_init') #4 /usr/www/users/konopx/wp-admin/index.php(10): require_once('/usr/www/users/...') #5 {main} thrown in /usr/www/users/konopx/wp-content/plugins/only-tweet-like-share-and-google-1/tweet-like-plusone.php on line 552

After deactivating the plugin, it is okay.