"Call to undefined method stdClass"

[eluser]picklepete[/eluser]
Hello.

I'm currently doing some work on my site, allowing only certain elements of a page to be visible if the visitor is logged in. Nothing particularly difficult, just isset-ing variables.

Out of nowhere, I've gotten this error:

Fatal error: Call to undefined method stdClass::_assign_libraries() in /home/username/public_html/system/libraries/Loader.php on line 982

It only seems to show on one area of the site, and I can't pin what makes it so unique to that controller. I assume it had something to do with the fact I'm using regular php sessions, not CI ones.

Any ideas?