There is an error in the firstReq
url. It contains a whitespace character between "& scope". Try this (I just removed the whitespace):
public String firstReq = "https://graph.facebook.com/oauth/authorize?client_id="+API_Key+"&" +
"redirect_uri=http://www.facebook.com/connect/login_success.html&scope=publish_stream,offline_access,create_event";