[eluser]darkhouse[/eluser]
yeah, you can't use isset() on a function, $this->session->userdata('variable') is a function that returns a value or false if it's not set, so mvdg27's solution is how you do it:
Code:
if($this->session->userdata('variable')){
echo 'variable is set';
} else {
echo 'variable is NOT set';
}