ERROR: Cannot zero momentum of no atoms

Dear All,
I want to simulate a solid that contains different slides. I want to assign a different temperature to any slides. then let the system to exchange energy and become relaxed. But I see the following ERROR:

ERROR: Cannot zero momentum of no atoms (…/velocity.cpp:763)

Last command: velocity target12 create ${t2} 1234158

my input script is:

Does your target12 group have no atoms?
You can use print to output the value of a variable
which counts the atoms in a group.

Steve