You are using a 1D file for the '-input' option. You should use the '-input1D' option instead. That's the most salient mistake. Try that and see what happens.
Also, I strongly recommend you use the '-gltsym' option instead of '-glt'. In your case, it would be
-glt_label 1 "a-c" -gltsym 'SYM: stim1 -stim3'
which is somewhat more error-proof (doesn't require counting the 0s and 1s).
For more details, see
[
afni.nimh.nih.gov]
[
afni.nimh.nih.gov]
and for the advanced student, the contents of
[
afni.nimh.nih.gov]