Do you live in the UK?
If you have a communal dish then you probably have a distribution set up, from the dish, to a box, which then feeds 2 cables to each apartment.
Sky UK receivers don't have Diseqc switching capablilities, so if used with legitimate receivers, and subscription cards, then they wouldn't have to use Diseqc 1.0, to use the LNB's.
Try setting Tuner A to Simple, Single, Astra 2, 28.2E, and Tuner B to Not Configured, then try a scan.
Next set Tuner A to Not Configured, and Tuner B to Simple, Single, Astra 2, 28.2E.
If neither shows any channels, and the same message, try setting Tuner A to Simple, Diseqc A/B/C/D and select each option, in turn, and try a scan.
Please post back, with the results, and more information.