[eluser]CroNiX[/eluser]
The only time what I said wouldn't be true, is if you change the value of $config['subclass_prefix'], which defaults to "MY_".
The reason why it worked on the original posters development box but not his production box is because his development box's OS, presumably a windows or mac box, doesn't care about case sensitive filenames but his production box, probably linux, does.
About line 237 (CI 2.1.4) of /system/CodeIgniter.php, you can see it trying to determine if you extended Controller and if so, it requires it, so there is no need to manually include it and will actually cause an additional error if you do:
Code:
if (file_exists(APPPATH.'core/'.$CFG->config['subclass_prefix'].'Controller.php'))
{
require APPPATH.'core/'.$CFG->config['subclass_prefix'].'Controller.php';
}