Widget generating 404 page error

Hi,

When I click on the series link in the widget area I’m getting a 404 page error – this link generates a 404 http://stevendevonport.co.uk/blog/series/history/

I’ve disabled the plug-in for now but would like to get it working as I think it’s got great potential.

I’m running WP 4.1 and PHP 5.3.x

https://ww.wp.xz.cn/plugins/organize-series/