In message , Paul Corfield
writes
My guess is that the gates at South Woodford didn't let you out because
there was no recorded entry point given that you had travelled beyond
your zonal availability. The system needs to know where you entered to
calculate any pre-pay deduction as you could have entered at Zone 6 at
Epping or equally Zone 5 in West London.

Even under those circumstances, the gate will show a 24 code but will
open and he wouldn't have been able to use the Oyster subsequently until
the unresolved journey or Pre Pay debit had been cleared.
If Dave can remember the code which showed it might be possible to work
out what was going on. It's much more likely to have been a
communication error between the Oyster and the gate.
--
Kat Me, Ambivalent? Well, yes and no.