Just want to give you some information regarding this plugin , If it was not working for you i mean if you are unable to logged in automatically please check the iframe url in the page where you see this while logged in
Click here if your browser does not automatically redirect you. copy that iframe url and execute it in browser you have to see some thing like
cookie cutter executed successfully then only this plugin works across domains.Hope this help to some one

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And forgot to say you have to include the main domain name where you installed thie plugin and remaining domains in
Cookie Sharing Domains box where you want to share that cookie.
If you are unable to login into admin panel just clear your cookies of your browser and login again it will work.