yes the rivet script is a mel script... is the script save as zLineOfActionUtils.py on the same folder? you have to select your cluster and mesh then launch this command :
import zLineOfActionUtils as loa
import maya.cmds as mc
loa.auto_rivet_transforms_to_meshes( mc.ls(sl=True) )
the # Error: expected an indented block #
is a tabulation error from python when you copy the script from the forum to the script editor xD ...