OpenMEEG error #-1073740791

Of course you do: Running CAT12 deletes all the files in the folder.
Then you re-import or re-compute everything.
Nothing is left of the original template, but the MRI volume.

Running the computation of the BEM surfaces for the MNI template is indeed not recommended, as the MRI is cut too high, there is not a full head in this volume.

What you could try:

  1. First, restore the original template: right-click on Default anatomy > Use template > MNI > ICBM152.
  2. Create a new subject ICBM152_cat12, with "Default anatomy: NO".
  3. Right-click on ICBM152_cat12 > Use template > MNI > ICBM152
  4. Right-click on ICBM152_cat12 > MRI segmentation > CAT12
  5. At the end, copy the volume atlases or the cortex surface (for surface atlases) fromICBM152_cat12 to the Default anatomy folder.

In the future: do not delete the existing files of the ICBM152 template, this would bring all sorts of issues.