Membership issue with a theme I am using

Hi there,

I have the Membership Lite plugin installed on the following site:

It has a portfolio section, which for some reason doesn't quite work with this plugin (the theme support narrowed it down to the plugin).

When you click on the Portfolio page, there are three categories that appear. Clicking on any one of those links opens that category page and is meant to show the portfolio items linked with that category. However, nothing appears on any of those category pages when the plugin is activated.

Any help will be greatly appreciated.

Many thanks