Login to your WHM as root & access option Security Center >> Apache mod_userdir Tweak. Uncheck for DefaultHost (nobody) & click on save. Try accessing the temporary URL now. If you are hosted on a shared server, contact your web hosting provider.
IF you are using it for selling hosting avoid mod_userdir as it can lead to abuse and other issues, like if somebody buys an account with you and hosts a phishing site, he can spam your main server hostname/~username and in this way your domain will get blacklisted