[lammps-users] Group define problem~~

Hi all

I want to define a group of polymer atoms via ��region�� command. As following:

region range1 block 0.0 27.0 0.0 24.0 30.0 50.0
group layer1 region range1

But ��Error notice: Use of region with undefined lattice��.
��0.0 27.0 0.0 24.0 30.0 50.0�� is a range in unitcell. I use periodic boundary condition.
How to solve this problem?
Thank you very much!!