Hi both, thanks for the replies! (I'm replying with a new username, as I haven't been able to log in or retrieve my old one.) The plot thickens a bit when I try the 3dinfo command: When I use a recently updated version of AFNI (compiled November 21, 2014), I get this output:
NO-DSET NO-DSET
But when I switch to an older version (compiled February 24, 2014) I get this output:
Sub0043_Ses1_bld002_rest.nii.gz 124
Similarly, when I use that older version, afni_proc completes successfully! So it's looking like something that's changed between February and November in AFNI is causing the 3dAttribute error I'm running into.
Any ideas, folks? Thanks again for the help, all!
James