Can't Open The Sims 4

thekaffeehaus​  It's a bit confusing to me too, especially given the exact error you're seeing.  But this is also good news in that your computer overall is fine.  So what I would suggest next is moving the location of the Documents directory in your main account to a fresh folder.  This will test for issues with the current folder being used, and you can reverse it later if it doesn't help.  I explained how to do it here, the section about moving or restoring the location of Documents:

[CURRENT ISSUE] Sims 4 already running | EA Forums - 11818313

If you prefer, you can try the takeown command covered immediately below that section first.  I wouldn't expect it to help here, but then this error is odd in general, and it's not going to do any harm either.