[eluser]dsloan[/eluser]
Have you loaded/initialised the session before this? I'm assuming here it's
$this->CI->session which is undefined at this point.
However, having said that - if you're referencing this within a libary, then can you do some debugging and check just exactly which part of that is causing the problem, i.e. which is the non-object, $this->CI, $this->CI->session...
But you say this was working previously so I assume you know all this already.