What is the cause of this Facebook error: "An error occurred with PHP SDK Unit Tests"?

I'm working with Facebook login on my website and was looking at this example: https://g开发者_Python百科ithub.com/facebook/php-sdk/blob/master/examples/example.php

When I hit "Login with Facebook" on the example site, I get an error:

An error occurred with PHP SDK Unit Tests. Please try again later.

Any ideas why this would happen?

I was facing the same error earlier (now resolved). The mistake I made was calling Facebook API using old method i.e.

$appid = 'xxx'; 
   $secret = 'xxxxxxxx';
   $fb = new Facebook($appid, $secret);
   $user = $fb->getUser();

Here $fb instance itself was not correct. I checked it by checking

if ($appid == $fb->geAppId())

TO FIX IT use the new method of API

$appid = 'xxxxxxxx'; // your APP ID
$appsecret = 'xxxxxxxxxx'; // your APP sceret. 

$config = array(
    'appId'=> $appid, // IMP: note that it is 'appId' and not 'appid'.      
    'secret' => $appsecret
    );

$fb = new Facebook($config);

printf("<br/> FaceBook AppId Test : %s",(($fb->getAppId() == $appid)?"PASSED":"FAILED")); 
printf("<br/> FaceBook Secret Test : %s",(($fb->getApiSecret() == $appsecret)?"PASSED":"FAILED")); 

Above two printfs are only for testing purpose if $fb itself was created correctly or not. You might want to remove these in your application.

There's a chance that your localhost has issues interfacing with the external servers.