MarkAB is your site on a public server somewhere I can log into the CMS and check the data from? You can email me will@silverstripe.com your details if you don't want it public.

Thanks Willr for helping me sort the issue out - it's really appreciated!!

For anyone else who may be experiencing the same thing, download & install the latest trunk version of the forum module it solves the problem.

*Reminder: Save a copy of your old forum css file to re-upload after the installation!! ;)