The CAT12 segmentation/import functions are in the middle of major rework, I'm sorry for the bugs that are pushed to the main distribution...
Reporting them is very helpful for making the code more stable, thanks!
This commit should fix this the CAT12 import error (among many other things, like handling the non-linear MNI registration in the MRI viewer):
Anatomy: Handle non-linear MNI normalization with SPM deformation fie… · brainstorm-tools/brainstorm3@29ef6a3 · GitHub
This process is split in two: the segmentation done with CAT (which terminated correctly in your case) and the import of the output done by Brainstorm (which failed).
During the next few months of test phase, it can be a good idea to save the CAT segmentation folder (in the Brainstorm temporary folder: $HOME/.brainstorm/tmp/cat12). Make a copy of this entire folder (the output of CAT), outside of the brainstorm/tmp folder, which is emptied every time Brainstorm is started. If you need to wait for an import fix, or if you need to reimport your subject later, you'll be able to import it with the menu "Import anatomy folder".
The second bug, I will try to handle more gracefully, so that it returns a more readable error message.
In the Brainstorm protocol you sent, I could see that what you are trying to process are not real MRI volumes. One is a full-head volume with a contrast that really doesn't look like a T1 volume (which are required in input of the volume segmentation techniques available from Brainstorm), and one contains only the brain (no skull, no scalp), there is therefore nothing to run the segmentation on.
I fixed the bugs, but this not going to make your segmentation return anything meaningful. If you want to use this anatomy template, you should ask its provider to share a FreeSurfer/BrainSuite/CAT version of them, in order to use them in Brainstorm.
Otherwise, you can use the Oreilly infant templates available in Brainstorm.
https://neuroimage.usc.edu/brainstorm/Tutorials/DefaultAnatomy#FreeSurfer_templates