franklau,
The "Kunena - JomSocial Integration" plugin isn't from JFBConnect. I'm not sure what that is, but memory allocation errors are an indication that you have more extensions (plugins, components, modules) enabled than the server can handle with the amount of memory you are allowing it to use.
So, even though the error may be showing in the OpenGraph.php file, which is ours, it doesn't mean there's a problem in that file. It just means that by the time that file ie executing, all the other extensions have eaten up the available memory and our file is left with none to do what it needs to do. I believe at that point, disabling any other plugins may remove the error or at least make the error move to a different file.
Hope that explains how it's not really a JFBConnect-specific issue. What you can/should do is either:
* Disable any plugins you are not using and do not need. Especially system type ones, since they run on every page. That will free up more memory.
* Disable any modules you aren't using or don't need
* Ask your hosting company to increase the PHP memory limit from 25MB (it's current limit) to something higher, like 32MB.
If you have any other questions, just let us know, and good luck,
Alex