Can you look at the widgets page in the admin and tell me if there is an error on the fader widget itself? I think I may have found where the error is coming from, but as I said before, I have no issues on my testing server, so I have no way to test my theory.
The error is on every page in admin. When I deactivate S5 Image And Content Fader plugin, the error disappears.
Now the error is showing in the widget...