Sub-forum Page Sizing Issue with Sidebar

Hi

I'm encountering a strange issue on IPB4 - the Skin width is set to fluid and 95% which appears to be working intermittently on the forums. All pages are using a sidebar - the main forum index works fine, but *some* sub-forum index pages overlap the screen to the right. Others are fine. I've used the block editor to create the sidebars and *believe* I've used the same blocks. 

Index page (working correctly): http://forum.wegotserved.com/

Sub-forum index (working correctly): http://forum.wegotserved.com/index.php?/forum/32-home-servers-nas/

Sub-forum index (overlapping): http://forum.wegotserved.com/index.php?/forum/196-windows-home-server-2011/

Any help gratefully received!

Terry