I'm sorry and I wish that I could offer some insight into this error but Comcast it very tight lipped about what these numeric errors mean. The best advice I can give you is to try and go directly to the networks own web site and try and watch from there, I'm sorry to say that some programs are not available on the networks site for example BBC America does not offer streaming from their site so it's either Xfinity or nothing. This is a workaround only and not a real solution but other people have mentioned that the 517 error can correct itself after a time.
- Norm