Mapped Domains revert to the main directory

I have set this up on other sites and it works flawlessly, but for some reason I am having problems with this installation. I was using it in conjunction with the supporter plugin, but have since turned it off. It does not matter because the same thing happens either way. Whenever I use the domain mapping feature it reverts back to the root directory, main blog home page of the wp install url. Any ideas what could be causing this? I am not a real tech savvy guy so talk to me like you would talk to a child please. That is why I really like WP. I don’t have to be tech savvy. Thanks!