[Freesurfer] ERROR: dimension mismatch between input volume and seg

hi freesurfer experts

I am compiling the FA segment stats for several subject

I used mri_vol2vol --mov fa.nii --reg register.dat --fstarg ../mri/orig.mgz --interp nearest --o fa.anat.mgh

then I used:

mri_segstats --seg mri/wmparc.mgz --ctab $FREESURFER_HOME/FreeSurferColorLUT.txt --i dti/fa.anat.mgh --sum dti/fa.stats

for some of my subjects, Iam getting the following error:

mri_segstats --seg mri/wmparc.mgz --ctab $FREESURFER_HOME/FreeSurferColorLUT.txt --i dti/fa.anat.mgh --sum dti/fa.stat

$Id: mri_segstats.c,v 1.75.2.9 2013/02/16 00:09:33 greve Exp $ cwd cmdline mri_segstats --seg mri/wmparc.mgz --ctab /Applications/freesurfer/FreeSurferColorLUT.txt --i dti/fa.anat.mgh --sum dti/fa.stat sysname Darwin hostname psy-blackbird.ad.uwm.edu machine x86_64 user wieser UseRobust 0 Loading mri/wmparc.mgz Loading dti/fa.anat.mgh ERROR: dimension mismatch between input volume and seg input 256 256 192 seg 256 256 256

can you tell me how to fix this?

thanks Jon