I am using SPCascadeDropdowns. It works perfectly directly in my top site collection. However, when I try to implement it in a team site it does not work. Does anybody know why this would be happening?

Hi,

According to your description, my understanding is that when you use SPCascadeDropdowns in a team site , then it will not work.

I suggest you can track the web request using Fiddler, to see when you use SPCascadeDropdowns in the team site, the request data is valid.

Fiddler

Also, here are some code demos for your reference:

SharePoint Sketches: SPServices Cascading Dropdowns

Thanks

Best Regards