Hello Freesurfers!

I am working through the longitudinal tutorial found here:

To keep it simple, I ran longitudinal processing on 2 timepoints for one subject. My qdec file had only two entries. I would like to look at pct difference in thickness for one subject. I ran

long_mris_slopes --qdec qdec.dat --meas thickness --hemi lh --do-avg --do-rate --do-pc1 --do-spc --do-stack --do-label --time years --qcache fsaverage --sd $SUBJECTS_DIR

When I run the overlay I get an error saying that "the overlay cannot be loaded", although the file exists. 

freeview -f $FREESURFER_HOME/subjects/fsaverage/surf/lh.pial:overlay=$SUBJECTS_DIR/OAS2_0001/surf/lh.long.thickness-spc.fwhm15.fsaverage.mgh:overlay_threshold=2,5

First of all, is this method sound in order to visualize pct change in thickness for one subject? If so, why is the overlay not loading?

Best,

Ken