404 error message for a particular word in url

I am displaying different websites depending on the venue name. Etc. venue called "badbooking" then the url will be badbooking.school.com, but if the venue name contains a word "space", instead of displaying the site and the url, it gives 404 error message. Only this word, any other word works. It seems to be a reserved word, but can not find any related to it in the code

Any idea why is this happening?