I just got into the admin area to investigate this further. I'm not sure where the issue is coming from, but it's not specific to our SCLogin module or JFBConnect.
If you login (using any method) and then click the little logout button in the JomSocial toolbar on the right-hand side (the door with an arrow), you'll be brought to:
www.opotiki.net.nz/component/community/?Itemid=1
There is no menu item with an ID of 1 in your Menu Manager, so I'm not sure where that's being added from. The addition of that Itemid to all attempts to logout is the problem though, since the ?Itemid=1 is the only query variable Joomla can see, so it tries to use it to load a non-existent menu item.
I did update your Logout Redirection URL to JomSocials' home page, and that works properly (even though the Itemid=1 is still there). You could also use "Same Page", which would work whenever a user tried to logout on any page except your home page.
I hope that helps you narrow things down. I'm not sure what is inserting that Itemid=1 everywhere though.
Thanks,
Alex