Unable to login bbPress forum with mapped domain

Hi,

I have installed bbPress forum on my mapped domain at http://webstory.my/discussion/forum/webstory-support/, where webstory.my is a mapped domain of webstory.self.my. I found that there is no way for my visitors to sign in to the forum, please help.

I am currently using Firefox 10.0.2 to test.

Thanks.
Junior