Domain Mapping Plugin locks me into login page

I realize this is the second time I've come around on this, but I'm thoroughly stumped on this one. I feel like maybe I'm missing a step.

I set up my first mapped domain yesterday, and everything seemed to be working fine. The trouble occurred this morning when my client informed me that she cant' seem to log into her account. She blamed herself, figured she'd screwed up the login somehow, but I was suspicious, so I manually logged out of my network and attempted to log back. As before, I was asked to log in again, and my LLA plugin reduced the number of attempts I had left to try.

I went in thru FTP and pulled out the Domain Mapping plugin and everything went back to normal (except, of course, that her domain was no longer mapped).

I then turned off every plugin except the WPMU Dashboard and then reactivated the Domain Mapping plugin, logged out, and was once again locked out of the account. So, its doesn't appear to be a plugin conflict.

I deactivated the Domain Mapping plugin again so I could log back in. Now the only plugin running is the WPMUDev Dashboard. So, it must be a configuration error somewhere along the way.

So, RIGHT NOW, the set up is this:

The main website is

The mapped website is

All plugins except the WPMUDev Dashboard are off.

The sunrise.php file from Domain Mapping is the the wp_content folder.

The additions to my wpconfig file starting from WP_DEBUG are:

define('WP_DEBUG', false);

define( 'WP_ALLOW_MULTISITE', true );

define('MULTISITE', true);
define('SUBDOMAIN_INSTALL', false);
define('DOMAIN_CURRENT_SITE', '');
define('PATH_CURRENT_SITE', '/');
define('SITE_ID_CURRENT_SITE', 1);
define('BLOG_ID_CURRENT_SITE', 1);

define('SUNRISE', 'on');

Anything else you think I can check?