I've downloaded Freesurfer version 5.3 and signed up for a license. However, when I try to run the example:

mri_convert sample-001.mgz sample-001.nii.gz

I get the following error:

ERROR: Invalid FreeSurfer license key found in license file /home/john/freesurfer/license.txt

I'm not sure what to do here as I have the license file in the correct place and thought that I had obtained it correctly.

Best,