Problem

When starting the launcher, I get the error message: There was an error during startup. See the Log for more details

Suggestions

Reinstall Origin
Solution by Georgia82 for digital downlaods
Make sure your graphic drivers are up-to-date
Bypass the Launcher and start your game directly
Right click on the launcher icon and start your launcher as administrator
Make sure your Microsoft .net Framework is current
Put in the base game dvd or start the game from the base game launcher icon instead of the addon
If you uninstalled an EP make sure there are no left-over keys in your Registry. For information on Registry Keys, check this guide: Manually Uninstalling The Sims 3
Uninstall CAW and CAP and try to start the launcher. If that works, redownload the tools and reinstall them after cleaning your registry with CCleaner.
If you manually moved the game or part of it (don’t do that), the references in the Windows Registry are messed up. Reinstall your game.
If you installed your game on an external drive, there might be a problem with the drive letter. Make sure that your drive has a fixed drive letter.
Remove your User Files

This error often occurs after patching. Use the Patch Downloader for patching to prevent.

Create a Pet-Demo

If you have this error after installing the Create-A-Pet demo, please follow these steps

Go to your user files delete the following files:
- missingdeps.idx in DCCache (this is a cache file that will be recreated)
- buildMode_test_venkat_objects.package and buildMode_test_venkat_sims.package and world caches (it’s probably better to just move those files to your desktop and move back if you have troubles starting the demo after doing this. Remove again to play the game).
Start your game to see if everything is back to normal. If you have troubles with mising store content, check this post: Store and Custom Content uninstalls itself
Please also check this post: Create-A-Pet Demo