Upgrade Check While Installing on 2nd Computer

Hi, I am trying to install Photoshop CS4 on to a Mac Mini. I already have it installed on another Macintosh computer. I understand that Photoshop CS4 can be installed on just two computers. The computer I am trying to install it on to will be the second machine. When I get to the second step in the installation process after typing the serial number for my product, I am alerted to an "upgrade check." The message I get is:

We looked in the default locations for qualifying products installed on this machine, but none were found.

You may verify upgrade eligibility now by completing the fields to the right.

If you do not have access to the necessary information right now, you can go back to the Welcome step, and choose "Install on a trial basis." You can enter your serial number and verify upgrade eligibility directly in the product any time after installation.

If you require further assistance, please contact Adobe Customer Service for your region. For contact information, visit Adobe.com

Of course I do not have any previous versions of Photoshop installed on my Mac Mini, so I don't have any serial number to provide for this step. I do not want to "Install on a trial basis." I want to use the full extent of Photoshop CS4 as I purchased it. How do I bypass this upgrade nonsense so that I can install Photoshop CS4 on to my Mac Mini?

Thank you for your help.