Altamont Ravenard said:
It's usually a Reflex save to avoid the bad effects of Wall spells, so I can't see why in this case it should be any different.
Because the Reflex save for a wall spell is generally to get out from under it!
Walls of Fire don't allow Reflex saves; neither do Walls of Force.
Walls of Ice only allow Reflex saves to disrupt its formation - and only allow that if you are adjacent to where the wall is forming.
Walls of Iron allow you a Reflex save so long as those about to be crushed have "room to flee the falling wall."
You can avoid being entrapped by a Wall of Stone with a Reflex save - otherwise you get no saving throw.
Wall of Thorns does not allow a saving throw at all.
A Prismatic Wall only gives saving throws when you encounter a layer of the wall, not in general.
Note that, had the character in question merely been double-moving in the direction of the caster, there wouldn't be a problem - you can turn, stop, etc., as much as you want when double moving.
This situation only arises because the character in question decided to use the Full Round action Charge, which necessitates certain kinds of movement.