Im in the second Hlondeth quest, just finished the Thar (i think its Thar) war (i won :-) ) and talked to the girl in the weaponshop, and she asks me to get the chest inside Mystras Temple, but when i go to Mystras temple i find no chest

I looked everywhere for it, and the only chest in there is the chest near the priest who sells stuff, and i had already opened it before doing any quests in Hlondeth and the stars on the floor too.
Theres a door which cant be lockpicked there but i got no idea how to open it and my best guess is that the chest is there (but due to some weird install thing when i try to lockpick it it says something like "oh, sorry, do continue").
Is the chest really behind the wall/door? if yes how do i open it?
thx in advance
