If You have an issue with Facebook when loging into your vBulletin forum user or admin control panel, you may try to fix the issue with google. Search the error message it is giving You.

If you fail to fix the Facebook issue this time and want to make your logins working, what you need to do is:

- Disable so called "Facebook Connect" in your mysql database.

1. Login your hosting control panel and find mysql managing application like "PHPMyAdmin", when loged into PHPMyAdmin, find your forum mysql database name on the left and click it. Then on the right top click tab called "Search", then search for: enablefacebookconnect
Select table called "setting" for search and then Click submit/search button. Browse the result. Then you can see the line:

varname grouptitle value defaultvalue optioncode displayorder advanced volatile datatype product validationcode blacklist
Edit Copy Delete enablefacebookconnect facebook 0 0 yesno 10 0 1 boolean vbulletin 0

Click Edit.
Then in row "value", you need to changed it from 1 to 0. (from enabled to disabled)
Then scroll down and click Save/Execute or similar button. Then setting is changed. Now you should be able to login and Facebook connect is disabled.