Did some experimentation and found that it may be related to AdBlock, but in some sort of low-level sense. I turned off AdBlock, but now I recieve a 624 error (can't give the text here, but it's similar). It asked me to refresh and when I did, I received the old 422 error. Now I watch videos with IE 10 and mute the ads using the mute slider in the system tray. It's like watching ordinary TV now, but at least I can watch my programs.
Comcast, why don't you give some consideration to using a message along with obscure error codes? We (your customers) don't know what a 422 or 624 is. Would it be so hard to incorporate text along with the message (and something clear, not just "You can't play the video" - I think we've figured that out) You wouldn't even have to worry about I18N issues, just display the error and people can do the translation themselves. Heaven knows, "This video can't be played" is so informative.
Anyway, the solution (for me) was to go back to good old bug-ridden IE. Why? I have no idea. Just have some security on your system like Norton, Malwarebytes, Spybot, etc. I will scan now, but I am sure that IE will have a box of advertising cookies worthy of a Girl Scout troop.