Can't Upload a Specific Sims Family to My Gallery

I'm trying to upload one of my Sim families to my gallery, so I have them available to move into a new save. (Getting ready for L&D.) But for some reason when I go to do that, the gallery screen shows a blue wrench and gives the following message:

"This Gallery item was created using Custom Content that may not be available to you. Custom Content is not prescreened by Maxis. Use at your own discretion."

Here's the thing, though - I created this family from scratch (when I got the City Living expansion) and I don't use custom content at all. (I don't even know how to create my own custom content.) So, I'm hoping someone here may have some suggestions on how I can work around that CC warning so that I can get this family uploaded.

Thanks in advance for any assistance. 😊