Domain Mapping install problem

I am installing Domain Mapping onto a MU site. it is on a dedicated IP, I am following the instructions from the article today on WPMU. I have uploaded the plugin to public_html/, (unzipped of course), copied sunrise.php to public_html/ after I insert the line define( 'sunrise', 'on'); into the wp-config.php and then when I try to go to network admin dashboard and activate the plugin, I get blank screens. When I go back and delete the sunrise line in wp-config, site works. What am i doing wrong here? I am a relative novice with programming, but can navigate my way around cpanel ok.