I have a supercell having dimensions of about 6 A x 6 A x 30 A. It has 48 atoms out of which the central 12 atoms are fixed (local ordering). I am using MCSQS of ATAT to generate the SQS but it is giving error as below:

"Impossible to match point correlations due to incompatible supercell size"

I had followed the method given at: http://cniu.me/2017/08/05/SQS.html

Please suggest how I can resolve this error.