Can I use an upgrade key to install Parallels Desktop without previous version key?

Just now, I bought an upgrade key for Parallels Desktop 10 for Mac. However, the installation program needs a previous version key to confirm it. I've never bought a previous version PD. I thought upgrade key means the key for PD 10. Can I install it without a previous version key? Or the only way I can do is to buy another key of PD 9 for my upgrade key?

 

Upgrade key will only work in conjunction with previous version key.
What you need to do is:
1. Refund PD10 purchase
2. Buy full license key of PD9 at http://www.parallels.com/products/desktop/
3. If you purchase today, you will automatically fall under tech guarantee and receive your PD10 key a few days after: http://www.parallels.com/techguarantee2014/
Email us at cs@parallels.com to go through step 1 (and mention the link to this post). Thanks!

 

Thank you. It's helpful to me.