Hmm that's a bit odd. Did you check with Thurston Plunkett? Sometimes you have to go back to him to get the next quest. If not then go out to Base Camp and see if anyone has the next quest. I've never really heard of anyone having this problem in Celestia. Check to see if you can go to the Chancel cause that's the finaly place your able to go other then Celestian Sanctorium(Trial of the Spheres).