The Tooltip Glossary since version 2.6.0 requires the mbstring PHP module to be set. This is done in order to support UTF8 in a better way than before.
To solve this issue you need to install the mbstring module on your server http://www.php.net/manual/en/mbstring.installation.php
If you are using cpanel please check this link http://forums.cpanel.net/f5/enable-install-mbstring-module-158165.html
Posted in: TooltipPro