The room has been deleted, so only moderators and users with at least 10k network reputation can see it. (The user who reported being able to see it has 71k rep.)
Rooms are frozen when they become inactive, and some frozen rooms are automatically deleted. Your room had only a few messages and the system deemed it not worth keeping (there are a lot of rooms like that that people don't end up caring about). If you want access, I suggest you ask a moderator on that site if it can be undeleted long enough for you to copy what you need from it.