Recetnly i got following error when i was trying to access my facebook application/ iframe application. Invalid Argument Given URL is not allowed by the Application configuration.
The possible reasons could be as follows.
1. Trying to access facebook application directly (without facebook).
2. Facebook application ID / secrete key are wrong.
3. you are trying to pass the cancel_url to the facebook which is not permitted by facebook as its genereated by facebook only.