sEEG and ECoG give you information that is valid only for a few millimeters around the contacts.
Trying to reconstruct the activity of the full brain with a minimum norm solution is not really meaningful.
The most informative displays you can have are the signals themselves.
If you want to have a spatial representation of these signals, prefer simple interpolations on the cortex surface of the MRI volume:
https://neuroimage.usc.edu/brainstorm/Tutorials/ECoG#A2D.2F3D_topography
I've done also the Epileptogenicity tutorial, but unfortunately the process didn't work
Have you followed the tutorial using the example dataset provided in the tutorial?
What error do you get?