Invalid Callback

The contact form hangs after hitting send. The message is delivered, but the user experience is broken. Here’s the response I get:

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function ‘sf_send_mail_from_site_name’ not found or invalid function name in /home/colby1/public_html/dev/public/wp/wp-includes/plugin.php on line 214

{
     "mailSent":true,
     "into":"#wpcf7-f83-p376-o1",
     "captcha":null,
     "message":"Your message was sent successfully. Thanks."
}