I ran a successful dt_recon and then wanted to use 

mri_vol2vol --mov $subj_dir/dtrecons/${subj}.${cond}/lowb.nii.gz --targ $subj_dir/diffusion_recons/${subj}.${cond}/mri/aparc+aseg.mgz --inv --interp nearest --o $subj_dir/dtrecons/${subj}.${cond}/aparc+aseg2diff.nii.gz --reg $subj_dir/dtrecon/${subj}.${cond}/register.dat --no-save-reg

to get the anatomical segmentations into diffusion space. However, when running the above code I get the following error message?

echo subj =  AES139 , cond =  Rest

subj =  AES139 , cond =  Rest

set echo

cd /Volumes/DANIEL/dti_freesurf

mri_vol2vol --mov /Volumes/DANIEL/dti_freesurf/dtrecons/AES139.Rest/lowb.nii.gz --targ /Volumes/DANIEL/dti_freesurf/diffusion_recons/AES139.Rest/mri/aparc+aseg.mgz --inv --interp nearest --o /Volumes/DANIEL/dti_freesurf/dtrecons/AES139.Rest/aparc+aseg2diff.nii.gz --reg /Volumes/DANIEL/dti_freesurf/dtrecon/AES139.Rest/register.dat --no-save-reg

regio_read_register(): No such file or directory

Could not open /Volumes/DANIEL/dti_freesurf/dtrecon/AES139.Rest/register.dat

Matrix from regfile:

MatrixPrint: mat = NULL!

No such file or directory

I have attached an example register.dat file in case that is the issue.

also the output for ls -l register.dat

-rwxrwxrwx  1 administrator  staff  323 Feb 18 13:59 register.dat

Any advice with troubleshooting is greatly appreciated!

Best,