Yes, got the same thing on my iPhone 3GS iOS 4.2.1. I tried to remove and reinstall facebook, but it fails to connect saying "unable to connect with facebook. Please try again later". A little later, it shows the same "this build is only enabled for employees" alert message.
The interesting thing is that on my old iPhone 3G running iOS 3.1 it is running fine.
I hope facebook release a fix soon.