Airfoil on my Mac was working just fine until yesterday when I upgraded to the new version of Airfoil, and my Apple TV upgraded to the new version of iOS. Here is the detailed response:

Domain: SSAirfoilErrorDomain

Code: -1500

NSLocalizedDescription: RTSP Protocol Error

NSLocalizedRecoverySuggestion: Airfoil received an unexpected status code (Code: 406, Reason: Not Acceptable).

SSHTTPStatusCodeKey: 406

SSRTSPRequest: ANNOUNCE rtsp://10.0.1.6/3463682002 RTSP/1.0
Active-Remote: 1881643405
Client-Instance: 86747737FC0D68D6
Client-instance-identifier: F8F10F2D-993C-4E9F-B361-5F6835929CD1
Content-Type: application/sdp
CSeq: 2
Content-Length: 564
User-Agent: Airfoil/4.8.0 (Macintosh; N; Intel)
Client-computer-name: Victor’s MacBook Pro
DACP-ID: 45F0354B75646C6E

v=0
o=iTunes 3463682002 0 IN IP4 10.0.1.6
s=iTunes
c=IN IP4 10.0.1.2
t=0 0
m=audio 0 RTP/AVP 96
a=rtpmap:96 AppleLossless
a=fmtp:96 352 0 16 40 10 14 2 255 0 0 44100
a=rsaaeskey:Gr8qH5+zsUtaMxUYMMgoZQbqt06ALtW7FD916WSnEBW8mRNypyRO13a4D5bUaVH2HOcYHYNO49jAn6zmIJo4IpdqBAkVXqLfSQAU3WlPJxleLJhNtMJv/yn0v8gD6lFBZhhDhxgHyUCrYbI63SZhSoZv8aiFyh/RE1XQFmDsbt/QzkjIWy5zXbkPNX227UP7/b1s9gwRbPYVmD29fyt3cjhJageU64hTDAOYgECQ6TCo9zQMoRTNQzdQLpcxfoDLctGuBZExByyoBEkroh0cD+JQFKrO1aPf5g9HWF9Gqo0cGrrb9JknPjYPoI0Rr3uegjU717+R1WippeQJiIporw
a=aesiv:AAECAwQFBgcICQoLDA0ODw

SSRTSPResponse: RTSP/1.0 406 Not Acceptable
Content-Length: 0
Server: AirTunes/190.9
CSeq: 2