Changing email address from profile

Hi,

When I changed my account profile's email address to a previous email address that's been used before I get the message "email already registered" and it won't let me use that email address as the email that is attached to main user. 

Thank you!

Account: gac

I have checked your account and see that it is currently registered using the email address jpolicarpio@gac.com. If the other email address is already registered for another account, it is not possible to use the same email address for another account. Please let us know the email address that you want to change, so that we can check and assist you further.

Thanks!