Oops, I spoke to soon
It seems the mod is not allowing my forums to shrink in width depending on what screen resolution the user has i.e. if a user has 1024x768 then the forums go off the right edge causing the horizontal slider appearing for the user to be able to see the right side of the page.
The line that is causing it is:
HTML Code:
<div id="ajaxTFHcontentarea" style="border:0px solid gray; width:100%; height: 100%; background-color: white; padding: 0px"></div>
-- EDIT --
Spoke to soon again 
I am using the Cyb - Sub-Forum Manager mod and I didn't realise that my sub forums were being pushed across the page causing a blow out in the overall width of my site - made the amendments as per https://vborg.vbsupport.ru/showpost....&postcount=566 and all is working great - thanks!