Can you tell us more about the error? Which tool were you using? unpacksdcmdir? This might be better on the
freesurfer mailing list.
You might try converting the DICOM files to NIFTI via AFNI tools (e.g. Dimon) using a command similar to:
Dimon -infile_prefix path/to/dicoms/MR.* -dicom_org -GERT_Reco -quit
Alternatively, you could use
dcm2nii or
MRIConvert.