If it is a valid license file you have all the correct conditions. My only guess is that somehow the license file itself has been damaged. Send mail to firstname.lastname@example.org
with enough info for Scott to identify your sale and he will replace the license.
The license has no version restrictions, expiration etc.
2.79 is an old version with known bugs, please upgrade to the latest version found in this forum. This will not effect your license issue.