[Freesurfer] thickness and make_average_subject

Hi all, I am using make_average_subject to generate average subjects for two groups in a study. The average subjects' surfaces are created with no errors. However, I am curious why I cannot get the thickness file generated to appear on the surface. After I have the inflated average surface open, when I try to load lh.avg_thickness I get the following error:

% ERROR: number of vertices in /space/troy/5/users/MEGfiles/MEGdata_raw_st im14fix/allsubavg/surf/lh.avg_thickness does not match surface (136768,163 842)surfer: error reading curvature file

Am I just trying to load this incorrectly, or could there be some other reason why the thickness file will not load on an average subject? Thanks in advance, Cameron