We are pleased to let you know that this issue has been fixed. You should now be able to access the game without getting the error. ---------------------------
Why am I getting the "It look's like you've opened up Farm Ville 2 in another window!" error message?
We heard that you're unable to access the game due to the error saying FarmVille 2 was opened in another window.
Our team is aware of the issue and it will be corrected soon. There is no need to write to support about this.