Outright Photoshop purchase in 2013 now being held hostage

1. Remove Creative Cloud with the Cleaner Tools.

2. Restart your computer.

3 Re-install CS6 with your original disks or downloads.  Enter your serial number.

CS5 and CS6 are on life support. But they can still be activated.

NOTE 1 : Creative Suite installers won't work on macOS Sierra, High Sierra or Mojave without terminal workarounds. See the help article below.
https://helpx.adobe.com/creative-cloud/kb/install-creative-suite-mac-os-sierra.html

NOTE 2: Legacy Creative Suite will never run on Catalina or Big Sur. Only the latest Creative Cloud products are compatible.

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Beware of fake Adobe reps who may contact you privately offering to sell you software or take control of your computer. It's a scam, run away!  Real Adobe employees will NEVER reach out via Outlook, Yahoo, Gmail or Skype.
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3 Easy Ways to Identify Genuine Adobe Staff
https://tinyurl.com/10791730

Yes. If you have CS6 and install CC on the same machine, CS6 can be updated to a different version to the standalone perpetual licensed version. You should be able to deactivate, uninstall cc and CS6, redownload from your account, reinstall and reactivate.

Dave

Hi

You made need to use the Adobe cleaner tool to remove the CC part from you PC, it has been known to cause issues with activations of pre CC Adobe apps like Photoshop

https://helpx.adobe.com/creative-cloud/kb/cc-cleaner-tool-installation-problems.html