[eluser]InsiteFX[/eluser]
Any Class that is in th systen/core directory that is extened has to be placed into the application/core directory. These are Core Classes.
MY_Controller is extending the system/core/CI_Controller, as you can see this is a Core Class.
Any Class that is extended that is in the system/libraries directory has to be placed into the application/libraries directory. These are Library Classes.
InsiteFX