Ok, some info about Barnabus chest. From game script:

IT_KeyType_E
DZ_NecroCave_Key1
DZ1
DZ_Necromancer_Cave
0
DZ_NecroCave_Chest1


IT_KeyType_C
DZ_NecroCave_Key2
DZ1
DZ_Necromancer_Cave
0
DZ_NecroCave_Chest2


Looks like we have two keys in the Cave, but I've found only 1 0_o