I don’t know if this is known to other users, but the 3D warehouse has been acting strange. Below are some images demonstrating the randomness of these errors. While I don’t know what could be causing this, it looks to be a number of issues, since it’s giving random notifications about unspecified issues.
I’m not exactly sure what this means, but is the 3D Warehouse going through another overhaul phase? If the 3D Warehouse is still being ironed out, that would be helpful to know.
Exactly what problem are you encountering now? Your profile indicates you are using SketchUp 2016. Is that still true? If so, you should be aware that the 3D Warehouse only supports downloading files for the latest three versions of SketchUp. So that is SU2017, 2018, and 2019. For earlier versions of SketchUp, you can go to the 3D Warehouse in your internet browser and download the Collada file which you can then import into SketchUp.
As I wrote, the only SketchUp model versions now available will be for SU2017, 2018, and 2019. You’ll need to download the Collada file for earlier SketchUp versions.