$_GET values

[eluser]Craig A Rodway[/eluser]
The $_GET variable is not allowed/supported. from the User Guide - Security.

GET, POST, and COOKIE Data

GET data is simply disallowed by CodeIgniter since the system utilizes URI segments rather than traditional URL query strings (unless you have the query string option enabled in your config file). The global GET array is unset by the Input class during system initialization.

Interesting thread here also.