I have issue after upgrading my wordpress to 3.6 see below for errors which displays on wordpress admin panel not on front of website.
Warning: call_user_func_array() expects parameter 1 to be a valid callback, function ‘regis_options’ not found or invalid function name in wp-includes/plugin.php on line 406
Warning: Cannot modify header information – headers already sent by (output started at wp-includes/plugin.php:406) in wp-includes/option.php on line 571
Warning: Cannot modify header information – headers already sent by (output started at wp-includes/plugin.php:406) in wp-includes/option.php on line 572