Andy,
The following is the same response I just send in the answer to your Contact Us email:
Generally, this is caused when the Open Graph tags are not set on the page as you're expecting. Facebook (and other social networks) build the images to be shared based on these tags. JFBConnect provides multiple ways to set the og:image tag, so please read how to set the tags at
www.sourcecoast.com/jfbconnect/docs/open-graph/tags-for-joomla.
However, if you do believe the tag is set properly on the page, it's possible that there is a communication issue between FB and your site. Please see the "My Share Preview is Incorrect" topic at
www.sourcecoast.com/jfbconnect/docs/common-support-questions in this case.
Let us know if you have any questions.
-Melissa