I've added the standard addthis code snippet, as I have for several other sites. But on this particular site, when the buttons are clicked, the url is passing NULL, and breaking the link.
This is the site: http://www.ecehh.org/
Here is a screen grab showing null in the URL.
I've checked the pages for script errors and there are none.
I've checked another website I've built that uses it, and it working fine with pretty much identical code.