Is there a bug in the Domain Mapping plugin that you know of?

After installing the DM plugin and adding SUNRISE to my wp_config file I have problems loggin in to my Wordpress site. Initially it works and lets me map my domains, but when I log out I can't get back in and get the header already send message. My hosting company has installed a brute force protection plugin for all its wordpress sites and now I wonder if the Domain mapping plugin is in conflict with it or if there is a bug in the DM plugin.

Many thanks in advance, Ryan