Ok, so we turned on the TV and the STB in the bedroom today and there was a white box covering the screen saying we have to reset our PIN.
I thought it was the TV until I tested the DVD player and - no white box!
I fixed it by doing the online reset of that STB - worked like a charm (the second time) - no more PIN reset message.
Just in case anyone else has this, it is a large white box with a heading saying you need to reset your PIN. There are three choices:
Enter/Reset PIN
Disable PIN
Cancel
The cursor doesn't move and nothing you do will clear it. The online reset works.
Just an FYI.