1. Install the script as you get it.
2. After installtion, when you want to login in admin, it will say invalid licence key.
3. now unzip "License_6.0.zip"; you will find a file inside "License.php".
4. Upload "License.php" to your site root (script folder root in your server) and overwrite existing.
5. Upload again the same file "License.php" to SITE ROOT/includes/classes/WHMCS folder and oerwrite existing.
6. It is all, you can access now admin area.