This is a problem that stems from Facebook and there isn't a way for us to react to all the bugs and problems they introduce, because often in a matter of a week they either fix it, or the error is different.
Moreover, the Share button is deprecated and it was present in the control only because of the requests we received for it. You can see it is already deprecated in this article: http://developers.facebook.com/docs/reference/plugins/like/
(see the What happened to the old Share button section). Even their link to the share button documentation is now dead (it leads to a different page).
We are currently looking into this functionality and if possible we will implement some workaround for this, but it seems like facebook are silently removing the share button. If you look in the net you will see many more people having the same problem, and it is made even more complex in the RadSocialShare context because we need to support AJAX scenarios and dynamic script and markup generation with scripts that we cannot actually control.
All that being said, what I can suggest is that you use the recommend button or the like button (from the Standard buttons) or the Styled facebook button.
On the subject of the non-working button in our demo - when the control and the demo were created this was working as expected and the fact that now it isn't is due to yet another silent change Facebook have introduced and is out of our control. Currently our only option is to wait and see if they will fix it or we will be forced to remove it as well.
the Telerik team
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