I have same error, its plugin drag-drop-featured-image.
[13-Jan-2015 22:13:50 UTC] PHP Notice: Undefined offset: 0 in D:\WWW\Web\projects\wordpress\wp-content\plugins\user-switching\user-switching.php on line 655
[13-Jan-2015 22:13:50 UTC] PHP Stack trace:
[13-Jan-2015 22:13:50 UTC] PHP 1. {main}() d:\WWW\Web\projects\wordpress\wp-admin\plugins.php:0
[13-Jan-2015 22:13:50 UTC] PHP 2. require_once() d:\WWW\Web\projects\wordpress\wp-admin\plugins.php:10
[13-Jan-2015 22:13:50 UTC] PHP 3. require() D:\WWW\Web\projects\wordpress\wp-admin\admin.php:124
[13-Jan-2015 22:13:50 UTC] PHP 4. require_once() D:\WWW\Web\projects\wordpress\wp-admin\menu.php:269
[13-Jan-2015 22:13:50 UTC] PHP 5. do_action() D:\WWW\Web\projects\wordpress\wp-admin\includes\menu.php:149
[13-Jan-2015 22:13:50 UTC] PHP 6. call_user_func_array:{D:\WWW\Web\projects\wordpress\wp-includes\plugin.php:496}() D:\WWW\Web\projects\wordpress\wp-includes\plugin.php:496
[13-Jan-2015 22:13:50 UTC] PHP 7. WP_Drag_Drop_Featured_Image->add_admin_menu_page() D:\WWW\Web\projects\wordpress\wp-includes\plugin.php:496
[13-Jan-2015 22:13:50 UTC] PHP 8. add_options_page() D:\WWW\Web\projects\wordpress\wp-content\mu-plugins\drag-drop-featured-image\index.php:218
[13-Jan-2015 22:13:50 UTC] PHP 9. add_submenu_page() D:\WWW\Web\projects\wordpress\wp-admin\includes\plugin.php:1216
[13-Jan-2015 22:13:50 UTC] PHP 10. current_user_can() D:\WWW\Web\projects\wordpress\wp-admin\includes\plugin.php:1138
[13-Jan-2015 22:13:50 UTC] PHP 11. call_user_func_array:{D:\WWW\Web\projects\wordpress\wp-includes\capabilities.php:1380}() D:\WWW\Web\projects\wordpress\wp-includes\capabilities.php:1380
[13-Jan-2015 22:13:50 UTC] PHP 12. WP_User->has_cap() D:\WWW\Web\projects\wordpress\wp-includes\capabilities.php:1380
[13-Jan-2015 22:13:50 UTC] PHP 13. call_user_func_array:{D:\WWW\Web\projects\wordpress\wp-includes\capabilities.php:989}() D:\WWW\Web\projects\wordpress\wp-includes\capabilities.php:989
[13-Jan-2015 22:13:50 UTC] PHP 14. map_meta_cap() D:\WWW\Web\projects\wordpress\wp-includes\capabilities.php:989
[13-Jan-2015 22:13:50 UTC] PHP 15. apply_filters() D:\WWW\Web\projects\wordpress\wp-includes\capabilities.php:1360
[13-Jan-2015 22:13:50 UTC] PHP 16. call_user_func_array:{D:\WWW\Web\projects\wordpress\wp-includes\plugin.php:213}() D:\WWW\Web\projects\wordpress\wp-includes\plugin.php:213
[13-Jan-2015 22:13:50 UTC] PHP 17. user_switching->filter_map_meta_cap() D:\WWW\Web\projects\wordpress\wp-includes\plugin.php:213