Salut, Clem-
Could you please post your version number of AFNI, and the exact command usage of @animal_warper? (Esp. for the latter, there are multiple ways masking can be done-- by automasking, or by template mask mapping.)
Also, can you please check what version of the NMT template you are (presumably) using? That would be provided in a README.txt file in your directory downloaded with @Install_NMT.
thanks,
pt