I was able to find the group that you're testing with from your image. It is public, which is good. However, as Melissa originally responded, JomSocial is inserting invalid Open Graph tags on the page. If you run that page through the
Facebook URL Debug Tool
, you'll see multiple errors.
Please follow
the instructions she posted above
which tell you how to clean up the Open Graph error messages that Facebook is detecting.
If you clean them up and the Debug Tool shows no errors, try again. If that still doesn't work, let us know and we'll gladly help investigate further.
Thanks,
Alex