Probably something in your mods folder not being compatible.
YOu need to find out what it is.
How can you figure out what it is that's causing it!? when you have over 3000 CC mods? this problem didn't start until I downloaded CC today and I THOUGHT I deleted it but it still gives the same message I'm starting to get pissed because I can't lose my CC ☹️😮
It's cc most of the time so mods ARE probably safe (but given we had a patch, you need to check on those anyways).
Remove the cc you've added last first, in groups, until it starts again.
Could be that a cc got borked with the update too and it's something you had for a while.
These are the fastest methods: http://modthesims.info/wiki.php?title=Game_Help:Finding_Problem_Custom_Content
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