Illegal offset type in unset (Session.php - Line 727)

What do you try to unset from session ?
The Key must be string or array of strings. Its most likely that you have send either NULL or other type which can't be unset ..

That's right.
Doing a $this->session->unset_userdata($data); where $data array contains keys that doesn't exist, throw this warning.

Thanks a lot!