why i have got same number of Jewel many many time.

[Tad Carlucci]

Duplicate objects are most often blamed upon simulator rollbacks.

Each simulator periodically saves its current state. If the program crashes, or the hardware fails, it cannot update that state, so the last one it did save is used. If, just before the crash, a gem, box, or other object (such as your favorite chair), appeared or disappeared, it's possible that same gem or box can be created again. It's also possible that cat, box, or chair you picked up will reappear, even though you also have it in inventory. This is often not even noticed, unless the item is No Copy, since it results in additional copies (violating the permissions systems contract for No Copy items); and how many copies of your favorite chair do you have in inventory already?

If you have a number of duplicates, from a few months ago, it sounds likely the simulator where the box appeared which produced the gem was having severe problems. If it still does, you should contact the Estate Owner, or just move to a better simulator.