Source: Redmine.org

For those of you who are running Redmine on Phusion Passenger, if you have certain versions of the RedCloth gem installed, you are in for some trouble.

I was getting something along the lines of:

Error message:
    superclass must be a Class (Module given)
Exception class:
    TypeError
Application root:
    /var/rails/redmine-0.7

This was on Ubuntu Hardy 8.04.1, with Apache 2.2.8-1, Ruby Enterprise Edition 080704 (I think), and Passenger 2.0.2, with Redmine from SVN-stable r1729.

A simple solution that worked perfectly for me was to remove ALL version of the RedCloth gem, allowing Redmine to use its own included version of RC.

gem uninstall RedCloth

One of the responses on that bug thread also indicates that gem version 3.0.4 of RedCloth is the most recent version compatible with Redmine, so you could also try using (only) that version.