Same issue here under iOS: Opening the keyfile and clicking "Copy to Boxcryptor" leads me to the "Sign In" screen instead of Boxcryptor Local on my iPhone 6. Using "firstname.lastname@example.org" displays the error message that this is not a valid user. I tried to copy keyfile from email attachment and Google Drive. There is no way to add the local keyfile and a provider.
Boxcryptor still works for me under Windows 7 and 10. Have used it for three years, but out of luck now on iOS 9.