What's the URL programmed into PayPal? When I hit cancel, I go through a few redirects on your page, starting with:
www.spikesantee.com/store/checkout-cancelled.html
This looks to be a registered URL as it always redirects to the Login page, regardless of whether I go there directly or from PayPal. I'd check the permissions on that URL again.
Not really sure what I else I can help with. I don't think this is caused by JFBConnect, but if you think it is related, definitely let us know how.
Thanks,
Alex