When you enter the CAS editing screen, it will load infinitely.

Try the following

• Close the game
• Rename Documents\Electronic Arts\The Sims 4 to Documents\Electronic Arts\The Sims 4_Old
• Start the game. All your content will be gone now as the game created a new folder. All your saves/.. is still in the old folder so not to worry. 
• Close the game again
• Copy JUST your save game from  Documents\Electronic Arts\The Sims 4 to Documents\Electronic Arts\The Sims 4_Old\Saves to Documents\Electronic Arts\The Sims 4 to Documents\Electronic Arts\The Sims 4\Saves
• Start your save
• Check if you still have the error
• Report back with your results for further steps on how to get your stuff back.