This is funny.
I was also getting message 721 on HBOW HD (504) and since I didn't have time to call D* this morning, I decided to leave them an e-mail through their website. This is the response that I received:
Thanks for writing about HBO West. I'm sorry to hear about the confusion this issue had caused. As of today, we are not yet carrying channel 504 in HD. For reference, here are the channels that we began broadcasting recently:
202 - CNN HD
212 - NFL Network HD
220 - Big Ten Network HD
247 - TBS in HD
265 - A&E HD
267 - Smithsonian Channel HD
269 - The History Channel HD
278 - Discovery Channel HD
280 - The Learning Channel HD
282 - Animal Planet HD
284 - The Science Channel HD
362 - The Weather Channel HD
518 - Starz Kids & Family HD
519 - Starz Comedy HD
520 - Starz HD East
521 - Starz HD West
522 - Starz Edge HD
538 - SHO Too HD
540 - Showtime HD West
544 - The Movie Channel HD
603 / 604 - VERSUS HD / GOLF CHANNEL HD
Thanks for your patience, and for giving us the chance to respond to your concerns.
Sincerely,
Aurora M.
Employee ID 100115079
DIRECTV Customer Service