Hi,
Due to some situation. I had to uninstalled and reinstalled facebook plugin, and now all of my facebook account users cant login to my site. It says:

Sign in with Facebook account
Your Facebook email is already in use on the site, please enter a password to the site to sign in or click cancel.

My users input the password that generated by facebook plugin and sent to their email, still no work. After click ok, nothing happened.
Now all of facebook accounts can not login any more.

Please advice,
Thank you and have a nice day