Looking at the code, that line is trying to generate the URL for the Comments box on the page. Is the FB comment box showing on the page even with the warning there? If it is, can you inspect it and see if the URL is pointing at the correct place?
However, the content plugin should only be used on Joomla articles and K2 items. I'm not sure why you'd be seeing this on a JomSocial page or a VM page on your website. Could you tell me a specific URL you're seeing this on? What versions of Virtuemart, JomSocial, Joomla and JFBConnect are you using?
Notice: Undefined property: TableCategories::$catid i
