Well, had the same "light on, did not record" error yesterday. I did some looking, and one tuner was not authorized, then the other was not authorized. So, on the phone with Shaw. After being on hold and whatnot, rebooting, pressing buttons and such, it was determined that the guide may be to blame.
Apparently, and this seems odd, the 630 has issues if the guide data isn't up to date. It may be trying to do too many things at once. I don't know, but it burned the early showing of Survivor and locked up during Big Brother (don't look at me like that, the shame is already very immense). If I record two movies late at night, no issues.