Strange that you're seeing this with every request. It's from the routine that runs at plugin upgrade. Is it possible that your DB is read-only?
You can probably solve this by doing a factory default reset on Wordfence: http://docs.wordfence.com/en/I%27d_like_to_reinstall_Wordfence_completely._How_do_I_do_that%3F
Bear in mind that you'll be deleting all your wordfence options.
We're investigating this further on our end.
Regards,
Mark.