Even in the errata, if you are using objective 1A then Walter can be placed in any space within 2 of any investigator.
Since the Ceremony Room is Sealed, and nobody can enter it, and only objective 1B triggers the 'all locks open' effect, then if an investigator is in any of the 3 basement rooms, the Keeper can just place Walter in the impregnable Ceremony Room and wait for the end of the event stack for an automatic win.
Thats pretty sloppy game design! (without the errata surely every Keeper put Walter in that room)
indeed if an investigator is within 4 spaces of that room then Walter can get there in a single move.
Why is this sealed room in this scenario? It makes it far far too easy for the Keeper - is it going to be errata'd or do i just have to house rule that if Walter enters that room he breaks the seal?
Indeed that seems a good general rule for sealed doors - a monster entering through the door breaks the seal - so the Keeper can't use such a room as a creature vault,