Could we get an actual explanation as to why the queue can't be used?

[seebs]

I had thought that error was what you got when the queue was full or there were too many people hammering the login server to process.

Why can the queue be "full" with under 10k people in it? Queues are super cheap, and are a very well-understood bit of technology. An 8086 with 640k of memory could handle a login queue of 5k users.