Sorted it. Within the last 24 hours Sky went from the O2 system - no username/password MER to Sky PPOA username/password required.
Normally running auto detect mode on the Asus set it to MER. But now, it goes to PPOA, and asks for username/password
That's why the supplied router worked, it showed PPOA rather than MER
Managed to find username/password, and worked.
Sky should inform the customers they're changing from one protocol to another...what if I did computer support at home and needed net connection?