Thanks for the URLs and for posting from your account.
The problem looks to be an IIS web server issue in dealing with periods in query string parameters. Basically, when a user clicks a link on Facebook to your site, they will add a lot of information to the URL (as you can see above) so that Google Analytics or other tracking software you may have installed can be used to help understand your referrals.
Specifically, in the URL is the following parameter:
If you change that in the browser address bar to:
It works.
You'll need to figure out why IIS is causing problems with the period in the query string, and unfortunately, that's not something I know much about. A quick Google search for "iis error with periods in query string" brings up a lot of results for this problem, including:
stackoverflow.com/questions/9336569/iis-...s-in-the-querystring
Hope that helps get you started, and let us know if you need anything else!
Alex