I had just the opposite this morning... All the SD channels had that message, but the HD channels were fine. We had to call though, and they sent an authorization number to fix it... Weird. Last night it was acting weird too. It kept searching for satellite signal on all the locals, but all the others worked. Never had these issues before last night. 622 by the way...
next time that happens, see if you can notice if the definition seems higher on the standard channels.... then when you powercycle (reboot) see if it degrades once the hd is back. This is what I noticed, and its bothering me.