Creating an average model out of several models by using the ShapeVariationAnalyser

Hi everyone,
I´m currently working with the ShapeVariationAnalyser Extension in the 3D Slicer version 4.8.1.
My aim is to create an average model out of seven vtk models, which have all the same amount of points.
I was processing the data according to the description:

However, after the computation of the mean group file, the right file for the “Morphological classifier” can´t be selected in the tab “CSV File mean”, so I can´t go on with further steps.

Did anyone of you had a similar problem and knows how to solve it? I would be very pleased for any kind of help!