It would help if you posted more of the output; as I said the script does normally setup PBC and images for you, so something unexpected must have happened before the error you posted. Does your system fulfill the stated assumptions for using the script, eg "PSF and coordinates from a system at least as large as the truncated octahedron have to be present"? One way to get this is to solvate your system in a sphere (solvate-sphere.str).

Lennart Nilsson
Karolinska Institutet
Stockholm, Sweden