9/12/2013 – 8:00am  —  Installed updates:
WordPress v3.6.1
NextGEN Gallery v2.0.21
Gravity Forms v1.7.9
WP-Slimstat v3.3.3

All three plugin updates caused errors when re-activating them on the test server.  Deactivating and then reactivating them again cleared it up.  If you notice any issues, please try deactivating then reactivating them to see if it clears the errors up for you before contacting us.