""Temporarily Offline." is a message the cable box gives when ever it can't turn into the station it has mapped for that channel. There could still be signal on that channel, just not enough for the picture to kick in.
If your getting that message on "certain" channels "all" of the time, then its probably the box needs to be reset to re-scan the channels, or there is a problem on just the frequency of certain channels. If your getting the message on random channels and sometimes they come in and sometimes they dont, then its more likly the signal strength is low going to that cable box.
First step is to check all cable connections at the wall and going to the back of the box. Then reboot the cable box. If this fixes it for a bit, but then it comes back, then its probably a low signal problem.To fix a low signal problem, you have to find out where the signal is dropping. To answer that I would need to know more about how the cable wire gets from the street to your cable box.