It means, AFAIR, that it cannot find the table that tells the box what channels it should be receiving. You mention that the conservatory was getting cold. If it was sufficiently cold and you moved it into the warm without letting the box get used to the temperature change before powering up you may have got some condensation inside the box. Not that likely as it probably isn`t cold enough but a possibility.
*Edit* Bugger, beaten by Punky while typing
