Hello,
To resolve your issue you need create custom template without sidebar for the page Forum. How to do this you can read at these links: http://premium.wpmudev.org/blog/create-a-full-width-page-for-wordpress-in-5-simple-steps/ http://www.expand2web.com/blog/wordpress-custom-page-template-no-sidebars/
Regards, Eva Kemp.
