I have been using the Flexible Upload D3Z Edition WordPress plugin for a couple years now on various sites that I work on or manage. To me it provides a much easier interface to upload images while building thumbnails on the fly than the default WordPress image media upload. The issue is the Flexible Upload D3Z Edition plugin has not been updated since WordPress version 2.6.X so it has broken on more than one occasion. So when upgrading to WordPress 3 recently it broke the Flexible Upload D3Z Edition plugin and below I describe how to fix the plugin so it will operate without issue in WordPress 3.X.
In the process of creating a mirror image of a current WordPress to be used for development purposes I ran into a PHP error that I had not seen before. The current version of WordPress was working without issue but because many of the settings needed to be modified for the installation to work with a different domain pointed to it. Even after modifying the settings that I had modified in previous instances to make WordPress work with an updated domain name I was still getting an error related to the WordPress Theme. I enabled some PHP error logging, started looking for answers on the web, and then implemented some changes described below to resolve the error.