Pfrancis817 please be aware this is a public discussion. I edited your post to remove the Photoshop CS6 upgrade serial number. The serial number is valid. I also show that Photoshop CS4 is the full version which you upgraded from. Have you tried entering the Photoshop CS4 serial number when prompted to enter the eligible serial number?
If so then I would recommend you begin the process of setting up the Macintosh again. This time when you migrate/transfer please only transfer your documents and settings to this computer. The migration process can lead to difficult to resolve errors. If you have already used the uninstaller and the CC Cleaner Tool then I don't have any additional suggestions to resolve this error.