There are 2 Cavernous Maws in Jugner Forest. One leads to an Abyssea area and one leads to a Wings of the Goddess area (Past Area). So it really depends on which Maw you are trying to access and where you are at in that particular story line as to why it is not working for you.
If it is the Cavernous Maw to the Wings of the Goddess (Past) area, you have to travel to that Maw on foot in the Past, travel thru it both ways to lock it in.
If it is a Cavernous Maw for the Abyssea Area, you do not have to do the enter/exit routine like the Wings of the Goddess, but you do have to have traveled to the Maw at least once on foot for the Abyssea Maw Teleport Guys to be able to send you to the maws. See link below for some general info on the 2 different Maws Skyfiredancer (talk) 05:51, December 14, 2015 (UTC)