I'm having trouble to moderate the comments

Can you tell me a bit more about what is, or isn't, working? Are you seeing the Moderate option? If you use it, what happens? Do you get an error, does the message never disappear, etc?

Other things to check are:
* Are you sure you're logged into Facebook.com with an user that is an admin of the Facebook Application you're using on your site? It doesn't matter if the user is an admin within Joomla itself.
* What version of JFBConnect are you using on the working and non-working sites? JFBConnect 6.4 upgraded to the new Facebook Comment box. That may be causing some issues. Let us know if the versions are different between the sites and we can investigate that further.

I hope that helps get you started, but if you have any feedback on the above or need more help, just let me know.

Thanks,
Alex

I am administrator fanpage on facebook

Facebook Comments aren't associated with a Facebook Fan Page. They are associated with the application that you made to allow for authentication on your site. They are different things and you may not be an administrator of both. Please go to the Facebook Developer Area and make sure you are the admin there. If so, then you should be able to administer comments.

I hope that helps,
Alex