This message means that there's a problem with satellite reception to the set top box. There are a number of possible causes including weather, obstructions, local cabling and dish alignment or wear and tear. For further information see Sky's help page >
Note that although you took the BT Sport package from us, it's your satellite TV provider who supplied you with your set top box and satellite dish.
If it's persistent and there's no obstruction, then it's likely that the reason you can't watch BT Sport or ESPN channels is due to the alignment of your satellite dish.
We're sorry but we don't install or maintain satellite TV equipment so we can’t check this for you. However support can be provided by local satellite TV installers, who you can find online or via your phone book.