You have likely been victimized by bad models from the 3D Warehouse . There is no quality control there, and many of the models are either absurdly over-detailed, contain features that are way too small to see, or are outright defective. Often this is because someone was modeling a single smallish object without context and wanted it to look good when viewed up close. Other times it is because someone took a very detailed CAD model and converted it to SketchUp. Other times someone was just showing off how ornate a model they could create. But the bottom line is that such models can overwhelm SketchUp when combined with other similar bloats, and in some cases the overwhelming leads to an error in SketchUp’s internal database such as what you are seeing.
I don’t know whether you did this, but you should always download a model from the 3dw into a separate file and examine it there to see whether it is good. Take a look at the model info statistics and decide whether you really need 250,000 faces for the playset. Unless you are going to zoom in very close to it, you will never see all those tiny faces!
What sink is causing the problem (there are an awful lot of components in your model, I don’t want to guess wrong)? It’s possible it is also hyper-detailed and is just the straw that is breaking the camel’s back.
Edit: Adam Billyard’s Goldilocks extension (available from SketchUcation’s plugin store) is an excellent tool for analyzing whether the entities and textures in a model have appropriate amounts of detail for the way they look in a particular view. It analyzes the density of edges or image pixels vs screen area and flags the ones that have way more detail than you can see.