I had the same problem when I first got my HDS. I think I discovered that I was copying and pasting the ID number in with dashes (although you don't see them once you paste the number in) and it made the number too long, so it automatically cut off the final two digits.
Has this happened here?
I called Slingbox and they helped. Also, you could emailing Echostar at: email@example.com
They are usually pretty responsive.