Hi Michael,

From my understanding the MRML function has been deprecated in favour of using ShapePopulationViewer (I believe one of the older posts on the forum says the same - at any rate, it hasn't worked for a number of versions and keeps giving MRML errors with no problem on the underlying function).

As for the vtk files, there are a few possibilities. Some of the intermediate files don't open with ShapePopulationViewer well (like the *para type files), but you can open them in the main Slicer window to see what they are. The ones you're after are the ones with surfSPHARM in their name (ellalign or procalign, depending - the documentation on what the different output files is in one of the wikis). Alternatively, if there is a failure somewhere along the processing pipeline then the VTK file may be there but the data in it is bizarre and so doesn't show anything in either ShapePopulationViewer or the main Slicer window. The first step is to check that the path to the original file hasn't got a typo in it! Otherwise if you're using your own data the object may have failed spherical parametrization.

Hope this helps,
D