As a security precaution, iMember360 doesn't allow regular Infusionsoft contacts to login using the same email address as that of an admin user.
In addition - and for similar reasons - WordPress does not allow two different users to share an email address.
These are the most likely issues when an administrator is suddenly no longer able to login.
The simplest solution is to change the Infusionsoft contact's email address, thereby eliminating the conflict.
Alternatively, you can change the admin user's email address. That can also resolve the conflict.
This safety measure is design to prevent account “hijacking”.
In some cases, none of the above may resolve the issue and you will still unable to login for other reasons. In that case, please submit a ticket using the support widget on this page.