Wrong Railcard code on a ticket.

[Be3G]

The only major journeys on which NSE is valid but GroupSave isn't are those such as London to Milton Keynes, Stevenage, or Bedford

GroupSave is valid on all of those! Though not with all available TOCs (e.g. no East Coast to Stevenage).

 

[island]

Well, yes. But only with a substantial time penalty.

 

[FenMan]

As an "unfortunate" who can only get a Network Card it is still good value for my journeys, which are mainly at weekends. I reckon I get the fee back within 2 months.