json error message on version 2.0.2.0

I am facing this json error message on my latest open cart version 2.0.2.0
On Installation it is running good. but after some days it gives error message, and not editing any order.
when i am changing order status pending to process the json error message pop up.
when i am trying to delete old order it is not deleting.

please find the attachment.
I am searching for solution but i can't find. please give me a solution.