I had a problem with my rewrite rules, that looked like this:

  DocumentRoot /var/www/trust.jj5.net
  RewriteEngine On
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteCond %{REQUEST_FILENAME} !-d
  RewriteRule (.*) http://trust.jj5.net/sorry.html [L,R]

I was trying to redirect any request which didn’t match a file or directory. The !-f and !-d requirements were failing because the path to the REQUEST_FILENAME wasn’t fully qualified. I fixed the problem by including the DOCUMENT_ROOT:

  DocumentRoot /var/www/trust.jj5.net
  RewriteEngine On
  RewriteCond %{DOCUMENT_ROOT}%{REQUEST_FILENAME} !-f
  RewriteCond %{DOCUMENT_ROOT}%{REQUEST_FILENAME} !-d
  RewriteRule (.*) http://trust.jj5.net/sorry.html [L,R]

Happy days! :)