Enable Facebook login into vBulletin site.

[npadbidri]

Hi,

I want to enable facebook login into my vbulletin website.

I have perform following steps mentioned into URL to ENABLE FACEBOOK LOGIN:
URL : https://www.vbulletin.com/docs/html/...acebook_enable

Now I am able to see the option for "LOGIN WITH FACEBOOK" .
When I click on this option it redirects me on FACEBOOK LOGIN PAGE.
But After successful login into Facebook , again I get redirected to vbulletin "REGISTER" page
instead of log-in into vbulletin site.

I have also set "Enable Auto-Register" to YES.

Same thing is happening with Registration /SignUp.

I wanted to know ,How vbulletin know that user is already authenticated by facebook?

Is there any setting which I missing out here? Please let me know those settings.

So any help would be greatly appreciated.
Thanks!!!