Updating from CI 1.7.2 to CI 2.0.0 - class CI_Controller not found

[eluser]TWP Marketing[/eluser]
If you have moved the system folder or application folder from their default location, you must change the setting in index.php for $system_folder and $application_folder to match the correct path of the new location.

Since you are not using the current version 2.1.2, be careful. I advise using 2.1.2. Read the User Guide that came with the version you are using and follow the upgrade path which it recommends