afni.nimh.nih.gov

I am attempting to use 3dSkullStrip on my images as it has been suggested that it should work better than 3dIntracranial. When I try to run 3dSkullStrip it brings up the error that the command is no recognized so it does not seem to be having an error running the command but does not recognize it as a legitamate command. Any suggestions on this problem?