I have just upgraded my WP to 3.8.1 and installed W3TC due to high usage problems with the hosting.
I also got the same error message as bdub8888.
When I de-activated the All-in-One Event Calendar by moving the plug-in file everything was fine.
Has anyone managed to get WP 3.8.1, W3TC and All-in-One Event calendar to work together?
Thanks for any help.