Error message in Open Graph Activity log..

That's normal. Until you've gone through all the steps in our configuration guide, actions won't be able to be posted to 'normal' users Facebook activity. First, you have to get it working with an administrator of your account and then submit the action to Facebook. Once they approve it, the actions will work for non-administrator users.

As long as you have the "Display Facebook API Errors on Front-End" setting *disabled* in the Configuration -> Facebook API area, your users won't know that you were even trying to submit on their behalf. If it's enabled, they'll see the same error message on the front-end.

Hope that helps explain,
Alex