I have one more information to let you know.
This error happens when I run the simulation which having a light cource more than three.
It works when I set one or two sources in the FDTD simulation region.
However, I have successfully ran the FDTD simulations which have more than three sources (or even up to 16 sources) in the institutions where I worked in the past.
I do not know why this does not works in my current working place.