GBA4iOS was released today at 3:45 PM ESTWithin 2-3 hours of it being released, Apple revoked the Enterprise Certificate allowing the App to install. Therefore, to install the app, you must set the date back to February 18, 2014 for the app to install. Once installed, you will be fine.
I figured I would make this thread before seeing several threads about the install for the app failing.
If you don't know what GBA4iOS is, here is the thread I made before it released: http://www.se7ensins.com/forums/threads/gba4ios-v2.1086750/