Undefined Guest index.template.php error

[pepa]

Getting the following error, does anyone know what it means?

Guest IP address 62.210.157.129   
Today at 04:27:45 AM
e925cf3e2006bc16526d54aaf8cfd9ff
Type of Error: Undefined
https://reformaps.org/forum/index.php?action=search2
8: Undefined index: title
File: /home2/reformaps/public_html/forum/Themes/default/index.template.php
Line: 443

I also get the same error message but referring to line 440.

lines 440 to 443 in index.template.php are:

<a class="', $button['active_button'] ? 'active ' : '', 'firstlevel" href="', $button['href'], '"', isset($button['target']) ? ' target="' . $button['target'] . '"' : '', '>
                  <span class="responsive_menu ', $act, '"></span>

                  <span class="', isset($button['is_last']) ? 'last ' : '', 'firstlevel">', $button['title'], '</span>
               </a>';

I'm running SMF 2.0.15 with responsive curve 1.

[Kindred]

some mod that you have installed is not fully defined