I have checked all the possible reason and found:
-I have no disease of any kind
-I have no bounty on my head, nor have ever been caught murdering/stealing
-My reputation is 23
-I am currently Warlock of Mages Guild, and have never been expelled
-I have just became Master Thief
-I am Spellwright of House Telvanni, and the first stage of my stronghold has completed
Strange thing is, I can still buy spells from her at discount price, and the disposition is still 98. I don't know why suddenly she decide to charge me double for travelling really...
Any help? Thanks.