Error register vbulletin 5.

[hienntp]

I did use the feature of logging in forum via Facebook, but I met an error.
As registering a new account http://forum.bkav.com.vn/register and after entering sufficient information and click ?complete signup?, an information appeared with the content as follow:
"Sorry, but the server is not responding properly to information requests. This may be a momentary problem. If you continue to receive this message and the site is otherwise functioning, please contact the site administrator."
https://vborg.vbsupport.ru/attachmen...1&d=1446796275
However, after I pressed the button F5, the account was still created.
This error only happened as I turned on the mode ?Enable Facebook Platform=yes? in admincp.
When I set the mode ?Enable Facebook Platform=no?, there was no error.
Could you please tell me the reason for this error?
I use vbulletin version 5.1.7.
Thanks.