'register_my_menus' not found or invalid function name

Dears all

I am the user of Newsmin themes. I have just installed wordpress 3.6 and then I tried to activate the Newsmin themes but after I activated the themes I got some errors as the following:

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function ‘register_my_menus’ not found or invalid
function name in /home/blabla/public_html/wp-includes/plugin.php on line 406
And then I also tried to login into the blog but when I opened https://site.com/wp-login.php, I got some errors:

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function ‘register_my_menus’ not found or invalid function name in /home/blabla/public_html/wp-includes/plugin.php on line 406

Warning: Cannot modify header information – headers already sent by (output started at /home/blabla/public_html/wp-includes/plugin.php:406) in /home/blabla/public_html/wp-login.php on line 384

Warning: Cannot modify header information – headers already sent by (output started at /home/blabla/public_html/wp-includes/plugin.php:406) in /home/blabla/public_html/wp-login.php on line 396

Thanks