Error 21 has returned. Again.

Does this stuff happen to Sims 4 when it's installed on Steam? I currently am using the EA app, but I am by no means attached to it. Oh, I forgot to add that I have NO mods installed. 

CovetCat​  What fixes have you tried?  What antivirus do you use?  Is OneDrive syncing your Sims 4 user data?  You can check in game—find the folder location, as described here:

https://sims4.crinrict.com/eng/2018/07/how-to-find-your-user-folder/

Let me know whether OneDrive is in the file path.  Please check even if you're sure OneDrive isn't present, since it can reenable itself after a Windows update.

I checked, and OneDrive is still disabled. The program is installed at G://TheSims4. The actual game data (Saves, Tray, etc.) is at C:\Users\carol\OneDrive\Documents\Electronic Arts\The Sims 4. I use Windows Defender, and EA is enabled many, many times. These things are all in place. I deleted localthumbnail.cache. I ran Repair Game. I attempted to add a pink flamingo to one of my lots in build mode, then clicked Save and Exit. Nothing. I went back in, and the flamingo was gone. Then the game froze up and I had to go into CTL-ALT-DEL to close it. I haven't uninstalled and reinstalled yet, because that didn't help last time.

Seriously, the prior two updates, I just left it along for a few days, came back, and it worked. I just can't keep doing that and hoping it will fix itself. So, in brief, I have disabled OneDrive, made sure that EA was cleared to bypass my firewall, ran a game repair, and, the prior two times, uninstalled and reinstalled the game. None of this worked initially.  Oh, and I moved everything out of my tray and saves folders to run it like it was new, but I couldn't get out of CAS to start a new save.

Am I missing something? It's just strange. 

CovetCat wrote:

The actual game data (Saves, Tray, etc.) is at C:\Users\carol\OneDrive\Documents\Electronic Arts\The Sims 4.

I'm guessing this is the issue.  Even with OneDrive disabled, having the user folder there can cause a variety of problems, including this one.

Sims 4 tries to use whatever Windows has designated as the Documents directory for this particular user account.  (Your computer will have several Documents folders, but only one per account is the directory.)  So the fix is to change the location of the Documents directory, then move your user data there.

The simplest way, if it works, is to open a File Explorer window right-click the Documents icon in the left panel (the special icon, not a regular folder), select Properties > Location, and change it from there.  The new path should be this:

C:\Users\your username\Documents

or a custom location if you like, but NOT a location on an external drive.  (That could and would cause other complications if the drive were disconnected or received a different drive letter at some point.)  Then start the game and make sure it's using the new location, then move your user data there.

If you can't move Documents the easy way, you can edit the registry instead, as described here:

https://learn.microsoft.com/en-us/troubleshoot/windows-client/shell-experience/change-personal-folder-location-fails

Don't change anything else, other than possibly Desktop and Pictures if they're also in the OneDrive folder.  Restart your computer afterwards and before testing the game.