Forum Facebook Like not linking to correct page
 

Ok, so my forum currently sits at www.site.com/forums. I set up my facebook app to reflect the relevant URL, but when I click the Like button, I get the URLs to the post being www.site.com/showthread.php etc etc... rather than www.site.com/forums/showthread.php

thus giving me a 404. Any ideas on what I may be doing wrong?