The map process for your custom map has most likely crashed or freezed, and no one will be able to access it until there's a server restart. When there is one we can't know for certain but there's one every once in a while.
It's a common problem regarding custom maps since the process gets started up more often than lets say an official map, since there's users in those pretty much 24/7. The more often a map needs to be started up, the more likely it is for it to freeze in this manner. This is more of a game problem than server, and booting off 700+ online users we usually try to avoid.