Sims 4 error message "missing or damaged game files"

@braxtanysue  Please uninstall Sims 4 and the EA App with Revo Uninstaller.  (The free version is fine.)

• If you have any saves you'd like to preserve, put aside your Sims 4 folder in Documents\Electronic Arts and rename it to something that doesn't include the words "Sims 4."
• Download Revo Uninstaller from here.
• Launch Revo, select Sims 4 from the list, and click Uninstall.
• Once the game is uninstalled, select "Moderate" under "scanning modes," and click Scan.
• Review the list, in case there's something you want to save; otherwise, click Select All, and then Delete.
• Close Revo, and restart your computer.

Uninstall the EA App with Revo as well.  I don't have instructions for that at the moment, but the process should be straightforward.  Restart again when you're done.

Install the EA App, then create a new folder into which you'll install Sims 4.  The folder should be on the root level of the drive of your choice, for example C:\Games is fine, but not C:\Program Files\Games.

If you use a third-party antivirus, disable it before reinstalling the EA App, and don't reenable it until you've tried to launch Sims 4 once.  As long as you don't do anything else on your computer at the same time, you should be safe.