+1 button misbehaviour

[omoutop]

I have added a +1 social button to our page.
Up to a few days ago it worked ok.
In the last few days it stops sharing page data (the +1 counter still working though) - we haven't changed anything to our pages/server configuration.

Clicking the button:
- increase the +1 coutner correctly
- opens a window where you get to see a page photo, title, descirption and be able to share it to your profile and circles (this isn't working - we get an "Error detected" message in the place where the page data should appear)

Can anyone help me to fix/debug this issue?

The button's html is:

<div class="g-plusone" data-size="medium" data-href="http://www.example.com/path/to/page">

And the js we use to load all of our social buttons is:

(function(doc, script) 
{
 var js, fjs = doc.getElementsByTagName(script)[0],
 frag = doc.createDocumentFragment(),
 add = function(url, id) 
 {
  if (doc.getElementById(id)) 
  {
  return;
  }
  js = doc.createElement(script);
  js.src = url;
  id && (js.id = id);
  frag.appendChild(js);
 };

 // Google+ button
 add('http://apis.google.com/js/plusone.js');
 // Facebook SDK
 add('http://connect.facebook.net/en_US/all.js#xfbml=1&appId=xxxxxxxxxxxxxxxxxxxx', 'facebook-jssdk');
 // Twitter SDK
 add('http://platform.twitter.com/widgets.js'); 
 // Stumbleupon SDK
 add('http://platform.stumbleupon.com/1/widgets.js'); 

 fjs.parentNode.insertBefore(frag, fjs);
}(document, 'script'));

the above code works on live site for the last 5 months without problems.