Search results 404 error if not searching from home page

Hi guys,

I have an error which is stopping me from displaying search results. This issue occurs whenever I do a search, thats not in the root of my site - and hence when searching from any other page, I get an error which goes straight to the 404 page.

Example error:

This works fine (as its from the root):

I don't have any issues when I'm using the default Wordpress search, so therefore it must have something to do with the search plugin I'm using:

Any ideas?