The warning in the Open Graph debug tool is correct, there are 2 og:url tags on the page. JFBConnect is adding one, but I'm unsure where the other is coming from. I know K2 has some Open Graph integration that we recommend you disable. Beyond that, you'll need to narrow down what is setting the additional Open Graph tags on the page.
To see for yourself, open the HTML on the page and search for 'og:url'. You'll find one tag at the very top that's not from JFBConnect and another block of og: tags about 20 lines lower that is from JFBConnect.
I hope that helps, but if you need more details, please let me know.
Thanks,
Alex