Facebook connect issue

Hello

I installed and configured the ultimate facebook plugin as instructed in the manual. However, when i click the login with facebook button, a pop-up window comes up and ask me to login to facebook - when i do so, the window goes away but the login is not happening... the page is not redirected as well.

Similarly, when i click refresh token in the plugin settings in the admin panel, a pop-up comes and vanishes.

What could be the reason?

thanks!
Arun