File does not exist: /usr/share/apache2/icons/ ...
Which was really odd, because my webroot is somewhere else completely!
Eventually I spotted a
/icons entry in the configuration for
mod_alias in apache, which intercepts all requests to /icons on any virtual host, and rewrites it. Err, thanks? Renaming the directory to "images" solved the problem in this instance, and I hope if you googled for an error message, you will find this page and be able to fix it equally quickly :)