I just installed image handler 2 on my site. After following the installation steps, I browsed to my store (shop.thebricktongroup.com) where I encountered this:

Warning: require(includes/templates/template_default/common/html_header.php) [function.require]: failed to open stream: No such file or directory in /home/.frowsy/bgroup01/shop.thebricktongroup.com/index.php on line 43

Fatal error: require() [function.require]: Failed opening required 'includes/templates/template_default/common/html_header.php' (include_path='.:/usr/local/php5/lib/php') in /home/.frowsy/bgroup01/shop.thebricktongroup.com/index.php on line 43

I know this is bad and it means I changed a file I shouldn't have, a change which I need to undo. However, I have no idea how to do this. Any help is welcome, thanks!

Nate