You're seeing this error because the server at http://cx.xaa.cc/checkgs.asp is taking too long to respond. By default URLfetch (the App Engine service which powers file_get_contents() on PHP in GAE when using a http or https URL) has a default timeout of 5 seconds.
Ordinarilly you can extend this to 60 seconds by specifying a timeout
in the configuration array, as follows:
$data = http_build_query($data);
$context =
array("http"=>
array(
"method" => "POST",
"content" => $data,
"timeout" => 60
)
);
$context = stream_context_create($context);
$result = file_get_contents($url, false, $context);
However in the short term be aware of this bug. https://code.google.com/p/googleappengine/issues/detail?id=9460