Category and Tag archives no longer working

I’m at the final debugging stages for a major web design project I’ve been working on for the last 6 months.

The site itself is based on the has become a bit of a behemoth (merging 4 existing sites into 1 massive one!) with various custom post types etc…

Getting to the point – my Category and Tag archives are no longer working, if you click on a category/tag in the sidebar while in any of the blogs, rather than take you to a list of blog posts within the same category/tag, it just goes to a list of nothing:

Example blogs:
http://whitewatergroup.eu/leadership-blog/
http://whitewatergroup.eu/women-in-business-blog/
http://whitewatergroup.eu/news-research/

Example category/tag archive:
http://whitewatergroup.eu/category/100-lessons-on-happiness/
http://whitewatergroup.eu/tag/positive-psychology/

I’ve based the site on this template; Carbon Light: http://otwthemes.com/demos/carbon-wp-light/

I’ve been wracking my brain for the last few weeks as how to get this working – but it’s beyond me – could someone be helpful and point me in the right direction as to how I’ve screwed this up somehow!