The first treasure chest to avoid is going to be inside Lowtown, right of Old Dalan's place. The second one you are going to find when you are going into the palace before you receive the Goddess Tear. There are actually several chests that are in the Cellar that you pass through, and you cannot open the chests that are in the southeast corner area. The Confiscatory, which is the sacred location where you receive your weapons and armor after capture, is also a place to avoid any treasure chest. Lastly, it is important to be aware of the Phon Coast. A single island has a total of sixteen chests, and one of these is the dangerous one. The best choice is to stay away from them as a group. If these four treasure locations have been avoided in Final Fantasy XII you can get the Zodiac Spear at the Necrohol of Nabudis.