I have installed the sidebar as instructed here

http://archive.ssbits.com/create-a-static-sidebar/

I then went in to try and change the 'external link' text and remove the header. I did this and then rebuilt the database (not sure if that was needed). Now my site is down and I am getting the error:

Fatal error: Class 'Page' not found in /var/sites/h/homelesshounds.org.uk/public_html/sapphire/security/Security.php on line 331

I have reloaded the original files back to normal but it has made no difference

HELP!