Hello mate
This can be a number of reason mostly though the channel has moved.
When you get this message are you selecting the channel from bouquets?
If so try select the same channel via the satellites menu
Press bouquets then green for satellites.
If it works this is because background scanning keeps your satellites section updated but bouquets are user files and are not modified.
You'll then need to highlight the channel if its working from the satellites menu press the menu button and transfer it to bouquets to update your old one.
Ferret