ReginaReyes Creating a new admin Windows account should have worked just as well, in that your previous Sims 3 user folder wouldn't have been in play. Did you transfer your old Sims 3 folder to the new account before testing, or install any content into the new folder? Or maybe the account wasn't local, for example could you have linked it to an email address? Or perhaps you tried some other troubleshooting step afterwards, like changing antivirus settings, and then needed a new user folder as well?
I'm not trying to say you made a mistake in the process. The idea for me is that understanding exactly how this was fixed, temporarily at least, will help me figure out how to address the ongoing problem.
If you play with no added content at all, do you still get the "serious error" the next day you try to play? I realize you don't want to go without this content, but it's a useful test.
As a side note, "custom content" refers to content created by third parties: CAS items, objects, anything that is not part of the game itself and isn't a mod. Content from the Sims 3 Store is called "Store content." I understand exactly what you mean, but this distinction may be helpful when googling for your issue or trying to explain it to someone else.
Also worth noting I did receive an error 16 when trying to save my transferred save but that was easily fixed by selecting save as instead, not sure if this was caused due to the copy/pasting from the old folder that was being updated with one drive
