[Freesurfer] Getting an Error at Watershed

FreeSurfer Support:

I am trying to execute MRI_Watershed and receive the following error:

******************************************* *********************************************** *********************************************** White matter intensity 0 is lower than CSF intensity 17. Please examine input images. Will terminate ... *********************************************** *********************************************** ***********************************************

********************************************************** MRIstripSkull failed. ************************************************************

What could be wrong with the input volume? How can I fix this? Any ideas?

Thanks, Alen