I’ve been able to verify that WP-Hive is at the very least one of the culprits, and that’s even without activating it. Just moving the Hive folder into the plugin folder will cause this error.
I had the same problem and was able to get back in by resetting the plugins folder as linked above, but if I try to revert I receive the error again. I am also running WP-Hive, so I’m curious what other people are experiencing.