If you are using the exact same CI setup on your development enironment (Where it works) and your production server (Where it doesn't work), then it is almost certainly something to do with the setup of the production servers PHP or Apache.
If you can, try and run phpinfo() on your dev server and production server and compare the differences between the servers.
At the least, try and run both on the same version of php.
I'm not sure on the minimum PHP version, but I know it works from 5.3+, but should work from 5.2+.
