With the release of WPChimp 1.3.2 we have decided that is time to stop supporting very old versions of WordPress.
For now, the details are a little fuzzy but we have planed to drop support for WordPress 3.x versions sometime next year.
If you are running an old WordPress version, please update your install by the end of January 2016 or disable the automatic update feature for WPChimp (you can do this from the plugin’s settings page in your admin panel).
This does not mean that the plugin will stop working completely, but we will stop testing with 3.x versions and we will remove a few lines of code from the admin panel.
If you need to downgrade to an older version of the plugin, you can download any version, at any time by using our download page: https://wpchimp.com/download.php
TL;DR: Please update your old WordPress 3.x installs by January 2016 or disable automatic updates for the WPChimp plugin.