1) First remove all gems
Code:

gem uninstall rails
gem uninstall mongrel
gem uninstalled fastthread

2) Now run cPanel’s Ruby installation script
Code:

/scripts/installruby

3) Now second command as required by cPanel
Code:

/usr/local/cpanel/bin/ror_setup

4) It seems cPanel’s “fast head” forgets to install, fast Thread
Code:

gem install fastthread

5) App’s don’t run still? – The issue in my case was outdated GEM! Mongrel did not want to run with the old version. So run:
Code:

gem update –system

6) Restart cPanel (not required but I like to do it)
Code:

/etc/init.d/cpanel restart