vannybananny This is the master thread for the "serious error" message, which includes how to safely get rid of OneDrive. You'll of course want to back up your Sims 4 content as well:
[Current Issue] Sims 3 "serious error" when loading save | EA Forums - 8322938
The fact that you haven't been able to register your Steam product codes has nothing to do with the error. If you want to have them added to your account anyway, contact EA customer support for help. I would strongly suggest using the live chat option rather than email. If you don't see it, try this link:
Make sure you're signed into an EA site (this one is fine) before clicking the link and that the location in the lower-right corner of the browser window is set to U.S. or U.K.
Alternately, try using the help site without being signed in. Some categories of issue allow you to proceed without an active login, and many of those offer the live chat option.
