“An App ID with bundle identifier X is not available. Please enter a different string” (Xcode 7.3)

Question

After updating to the latest build of Xcode 7.3 (7D175), every time I try to Export for adhoc distribution I get the above error. Everything was working fine up until the up

Answer 1

In my case nothing from above worked until I tried changing my bundle identifier prefix from

com.xxx.NameOfMyApp to com.xxxYYY.NameOfMyApp.

I must have accidentally picked a prefix someone else had already used.