About Script to calculate local diffusivity with Forcite

Dear all,
         Did someone try to calculate the diffusivity coefficient (D) of many water molecules (such as 100) using the script of local diffusivity calculation?   I  calculated the D of waters (about 113 water molecules) surrounding the polymer and I selected the surface waters (0~5 Angstrom).
       However, there was an error "There is more than one object in the "Molecule"s collection (function/property "Molecule") at -e line 147."  I don't know if I need to revise this script. Could someone provide some advices?  Thank you.