need urgent help with Ultimate Facebook error

When attempting to setup Ultimate Facebook I get the following error:
"Please, enter correct Facebook API settings and make sure Facebook app is public"

My Facebook application is public and I have used successfully with many other Facebook plugins that I have tried before, but for some season your plugging keeps giving me this erroir. I know both my ID and secret keys that I am inputting are correct and that my Facebook APP is public. PLEASE HELP