Earlier quoted context omitted.
That's not not a 404 page (missing page). It seems like it's supposed to be a 500 page (server error) or 503 page (unavailable) but it incorrectly returns a 200 status which means everything is OK. Edit: Corrected the 50X error information thanks to the responses below.
500 isn't server busy, it's server error.
503 (Unavailable) is more suitable for that I guess.