Hi Isabelle,
  I was not clear.  One should NOT add pickatlas (and SPM) paths with genpath.  The lines:

addpath(genpath('F:\spm12'));
addpath(genpath('F:\spm12\toolbox\wfu_pickatlas'));

actually add all the pickatlas stuff twice.  The more correct way would be:

addpath('F:\spm12');
addpath('F:\spm12\toolbox\wfu_pickatlas');
addpath('Other toolboxes that might need to be added to path');

Again, with SPM 12 all you'll be able to do is define ROIs.  I don't know if the results viewer works with 12.  ROI analysis through the "RESULTS" button won't work either.

Hope this helps,
Ben