Is CS4 compatible with Windows 10? [Branched, CS4 is dead]

This is a Windows 10 problem, not a Photoshop CS4 issue.

Try doing a Google search for "You don’t have permission to open this file. Contact the file owner or an administrator to obtain permission."

You'll end up with a load of possible solutions. Here's one that will probably work:

How To Fix “You Don’t Have Permission To Open This File” Error In Windows 10

Or if video is more your thing:

How to fix Photoshop "You don't have permission to open this file" error

You keep referring to the GAME.  What game is it exactly?

If the GAME to which you're uploading requires Flash Player to work, then I'm sorry to say that ship has sailed. Flash Player is officially end of life now.  As of January, web browsers no longer support Flash.

https://www.adobe.com/products/flashplayer/end-of-life.html

If CS4 will let you edit the picture after a restart, that would seem to mean that CS4 is working correctly

Not being able to upload is a different issue

CS4 is officially dead now.  The activation servers were decommissed so you cannot activate the software anymore.

Use modern software instead.

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