There is an error after undating my WordPress blog

Hello,
I have upgraded my blog to the version 3.5
After that on the Admin panel I see the message:
Warning: call_user_func_array() expects parameter 1 to be a valid callback, function ‘gpluspb_create_menu’ not found or invalid function name in /home/watchm/public_html/seo-content.biz/wp-includes/plugin.php on line 406
How to correct this mistake?
I’m not a programmer, so I avoid doing changes in the code by myself.
Can you suggest me the solution?
Thanks,
Nataliya