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Hi
I am attempting to create a group file using MRIS PREPROC 

My command is as follows 

mris_preproc --fsgd brainmorph.fsgd --cache-in thickness.fwhm10.fsaverage --target fsaverage --hemi rh --out mripreproc-rh-thickness.mgh

But I am receiving the error 

ERROR: dimension mismatch between *first two subjects* 


Would you be able to advise the cause of this error as I am unsure what is causing it

Thanks!