Looking at the line the error occurs the script is comparing one of your models with a verion of that model which does not exists, make sure you select all the models that do have verion information and exclude those with no version information.
Appreciate your response, Ciska.
I created a version (Options used are "Within the Selection" for both Connection & Assignment Handling and Assignment Level as "0") of a EPC model -- performed some layout changes onto this EPC and saved the same.
Subsequent to that I tried running this report -- that's when I get this error.
So the version do exist but the main differences between the model versions are likely to be the object positions.
Why does this script give this error, in this scenario?