Fatal error: Call to member function

Happens whenever a normal user signs in.  Does not affect Admin user.

 

Fatal error: Call to a member function canWriteToContainer() on a non-object in /SITE/com/mod/groups/start.php on line 833

 

Started on 1.8.0.1, upgraded to 1.8.1 hoping it'd fix it, but didn't.

Also ran garbage collector to no effect.