403 is "Access Forbidden". It can have a few meanings in this context, some of which are:
- Your authorization cookie has expired
- Their server is having issues and you are being directed to a non-public spot
- Based upon your authorization/location, you are not authorized for that particular stream at the moment
For 1, try manually rescanning in the DVR web UI. For 2, all you can do is keep trying or wait, because that's a "them" problem, not a "you" problem. And for 3, you can't do anything about it either; if it is 3—and occurring during live sports—I would hazard a guess that you might be in an area with a blackout.
(These are my ideas based upon what you have reported. I may be incorrect, but without more details, I cannot say.)