Overview

This error is almost always related to permissions: the game cannot access or create the Sims 4 folder in Documents > Electronic Arts. This, in turn, is typically due to an overprotective antivirus.

This guide is only for this specific error in Windows.

Workarounds

jump to: Change antivirus settings
jump to: New Windows account
jump to: Other suggestions

Change antivirus settings

The first step to try is to set exceptions/exclusions for Sims 4 and the EA App in your antivirus. Do so for all of these executables, or for the Bin folder that contains the Sims 4 .exe files:

TS4_x64.exe
TS4_DX9_x64.exe [only necessary if you want to use the DirectX 9 version]
TS4_Launcher_x64.exe
EADesktop.exe

This guide covers setting exceptions for Windows Defender, Avast/AVG, and Sophos:

https://crinrict.com/blog/2020/10/add-exceptions-to-anti-virus-programs.html

Other antivirus programs may work similarly, but if you're not sure how to set the exceptions, consult the online documentation from the publisher. Most offer instructions for this subject.

Once you've set the exceptions, clear the EA App's cache and repair the game (EA App > Sims 4 > Manage > Repair OR Steam > Sims 4 > Properties > Installed Files > Verify integrity of the game files). Then try again to play.

If this doesn't help, disable your antivirus, temporarily of course; as long as you don't do anything else while it's disabled, your computer should be safe. Repair the game again, and try to play. If this works, you've confirmed that the AV is the issue, and you'll need to dig further into its settings to find what's blocking the game.

If you can't play even with the AV disabled, please see below.

Either way, be sure to reenable your antivirus when you're done testing.

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New admin Windows account

It's possible that the problem is caused by a setting or broken permissions in your main Windows account, and the fastest way to test this theory is to create a new account. It must have admin rights (not a standard user account), and it must be local, as in, not connected to your Microsoft account.

To create a new account, open Windows Settings > Accounts > Family & other users, click "Add someone else to this PC" (under Other users, not Your family), click "I don't have this person's sign-in information," then "Add a user without a Microsoft account." Choose the username and password, answer some security questions, and you'll see the new account. Click it and select "Change account type" to make it an Administrator account if it's not already. It should say "Administrator - Local account" when you're done:

Click ctrl-alt-delete, select Switch user, and sign into the new account. Then open the EA App (and Steam or the Epic launcher if applicable) and try to launch Sims 4. You shouldn't need to reinstall anything. Your saves and other user data won't be available, but that's fine for the purpose of this test.

If Sims 4 works in the new account, it means the problem is contained to your old account. You can simply continue playing in the new account if you want. For any saves or other user data you'd like to transfer to the new account, sign into the old account again and copy the relevant files to C:\Users\Public. This folder is accessible from all user accounts; you can grab the files from there once you're in the new account.

If you'd like to fix your old account, please try the suggestions in this thread after the "new Windows account" section:

[CURRENT ISSUE] Sims 4 Unable to Start, Already Running | EA Forums - 11818313

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Other suggestions

If the above suggestions didn't help, please try everything else in this thread, which is for a distinct but related error:

[CURRENT ISSUE] Sims 4 Unable to Start, Already Running | EA Forums - 11818313

If those don't help either, please post in this thread asking for further help. Let me know whether you can play in the new admin Windows account or not: this is important diagnostic information.

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Forum Discussion

[CURRENT ISSUE] Sims 4 Unable to Start, Initialization Error