I have a site running the Group Buying Site plugin.
wp-admin/ takes me to to /account/login/ where I log in.
When the plugin is installed it seems to override that page with the 'Coming Soon' page.
I tried the fix you gave here: http://wordpress.org/support/topic/plugin-ultimate-coming-soon-page-a-new-login-page?replies=7
But it gives me this error:
Warning: preg_match() [function.preg-match]: Unknown modifier 'a' in /public_html/wp-content/plugins/ultimate-coming-soon-page/inc/config.php on line 40