406 Not Acceptable – Princely – Dreamhost

You get a ‘406 Not Acceptable’ response from the web server when you try to use the princely plugin for generating pdf on a Ruby on Rails application hosted on dreamhost.

Having tried the ‘Extra Web Security’ settings in dreamhost Web panel, and setting them on/off did not get very far.
Also setting up an .htaccess file didn’t seem to make any difference.
So the mod_security settings did not seem to be the cause of the problem.
Having a look at the apache error log files which in the case of the dreamhost ps are in /usr/local/dh/apache2/logs/apache2-ps_name it turns out that the problem was that the path for the prince binary was not setting up correctly in the file vendor/plugins/princely/lib/prince.rb on line 26.
A quick hack to make it work until finding the reason for the problem is to hardcode the path to the prince binary, so:
@exe_path = `which prince`.chomp
if @exe_path.nil?