Problems With Login ONLY on IE

Further investigation. I don't think it's the AddThis widget, it's a special file that we include in JFBConnect which improves compatibility and speed with Facebook integration specifically for IE. I can't access that file on your system for some reason, and if Facebook can't as well, that's why it's throwing the error. Can you check if the following file exists, and if so, why it can't be viewed from a browser:
Once we figure this out, it should fix you up.

Thanks,
Alex

If you don't immediately know why that file is breaking, you can try editing it and remove the PHP block at the top. All that needs to be in there is the last line with the script tags. The PHP block shouldn't be a problem, but we've never seen this issue before, so drawing at straws here.

Thanks,
Alex

Alessandro,
Glad we got you going and sorry for the troubles. Hadn't seen that issue before, so thank you for your patience.

As always, if you run into anything else, let us know, and we'll gladly help how we can!
Alex

Webatelier,
After a bit of digging, there's a few reports of this bug in Facebook's tracker:
bugs.developers.facebook.net/show_bug.cgi?id=19042
bugs.developers.facebook.net/show_bug.cgi?id=20168

There is the suggested work-around, but we can't test as we can't recreate it. If you'd like to try the fix, you'll need to modify the /system/jfbcsystem.php file. At line 162, you'll see the following:Modify this to add an additional line as shown below:
Let us know if that helps at all, or causes other issues.

Thanks,
Alex

Webatelier,
Sorry, the file is:
/plugins/system/jfbcsystem.php

Hope that helps, but let us know how it goes!
Alex

Webatelier,
Still a little stumped on this. We were out for a Joomla Day this weekend, and didn't have access to a IE computer, but we're back at the office now and can definitely recreate your issue.

More digging brought us to a more recent bug report of the issue, with a slightly modified fix. Don't know if it will help, as we can't recreate this problem on our sites.. but we'd recommend you try it as well. Similar to the above change to the jfbcsystem.php plugin, modify it like below (one additional line above the one you already added):

FB.UIServer.setLoadedNode = function (a, b) { FB.UIServer._loadedNodes[a.id] = b; };
FB.UIServer.setActiveNode = function(a, b) { FB.UIServer._active[a.id]=b; };

Try that out, and let us know. The change you made before looks like you implemented it right, so that's not the problem.

Good luck,
Alex