Hi, Osman-

I think that particular error message means that "$mask_dset" is somehow purely empty, and therefore it looks like nothing is there, and that "-setA" is the name of the mask dataset... which the code is having a hard time opening, hence the error.

So, I think you should verify that you have set mask_dset correctly---e.g., with a print statement prior to that?

Note once that is solved, you can use AFNI's gen_group_command.py to set up the ttest for you, writing the command to a text file (here, called cmd_ttest.tcsh), which you can then execute (e.g., "tcsh cmd_ttest.tcsh"):

gen_group_command.py                                 \
    -command 3dttest++                               \
    -write_script cmd_ttest.tcsh                     \
    -prefix out_ttest                                \
    -dsets $dirA/s01/s01.results/pACC.z+tlrc*HEAD                 \
    -subs_betas '0'                                  \
    -options                                         \
        -mask ${mask_dset}

--pt