Ultimate Branding plugin gives error "Are you sure you want to do this? Please try again."

I logged into my super admin dashboard today to change the graphics in the Ultimate Branding plugin. No matter which tab I select, I get a blank screen with a box that reads, "Are you sure you want to do this? Please try again."

I have tried logging out and back in, deleting and reinstalling the plugin, clearing my cache, using a different browser... I have no idea what else to try. The only non-WPMU plugins I have installed on the network are Google Analytics, Jetpack, and Widget Logic. Deactivating them didn't help either.

Any ideas?