http://wiki.ffxiclopedia.org/wiki/Infiltrate_Davoi

you cannot remove this mission if you have completed it by mistakenly pick it up again. you cannot do what the mission log in-game says to do, the npc dose not respond according to the mission information given. he does not give you a letter, he just tells you hes busy and keeps walking on his path in Davoi. i checked to see if Prince Trion would let into his quarters and nope and i tried this after the the server was fixed as well. i am already rank 4.. i wanted to take and repeat The Crystal Spring having the item(s) needed to gain more missions to rank up again.