You will get guide data even for channels which are impossible (on spotbeams outside your area), or unavailable for subscription (special and commercial broadcasts), so just because they show in the guide does not mean you can sub to them all, it is not an error, it is by design, which is why you can setup favorite lists to only show channels you can view.
When you tune to such a channel, it will give you a kind of 'error' code, which usually gives an idea of what type it is, some can be misleading,. like if you are on the east coast and are not eligible to get a west coast national feed, and try to tune to it, it will give 'Channel not Purchased', which may give someone the idea they CAN purchase it, when that is only true under certain conditions.