sims 3 there was an error during startup please see the log for more details

I had a similar issue- Try deleting your entire Sims 3 file (Hopefully you are ok will completely restarting, because that will happen- if you are sure it's not an issue with your mods or custom content you can take those out). Start up your Sims 3 launcher. Then exit out of it and view your EA folder- a new Sims 3 folder should have appeared. (If you saved files, I recommend not putting them back in until you have opened Sims 3 successfully.) Then, re-open Sims 3 and press play. It should work fine if you had my issue.

Hope this helps! 😳