Unfortunately, as PHP doesn't give a backtrace for fatal errors, it's hard to get more specific information. I've just searched the code for references to the function that is triggering your error and there's no way for it to be called via deferred.php by default. (It's actually only around to reduce backwards compatibility issues with add-ons originally built for 1.0/1.1.)
As such, I can only guess this is related to an add-on. Unfortunately, it's hard to figure out which one. It appears to be attempting to rebuild forum information. Any idea what this would be based on the add-ons you have installed?