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The domain of my website is alias one, visit the url like: http://forum.example.com/ will occur the error,
but visit url like: http://www.example.com/forum/ it works normally, I want to use "http://forum.example.com/" for my forum url, please help me!~
Have you installed your online forum manually? I would guess it has been installed by the hosting provider or an installer script provided by the hosting provider. That's not directly a Vanilla problem and so I think you wouldn't find anyone here who is able to support you, sorry!
OK, I guess the host provider provide the security messure.