Skinned models failing to load "could not load asset as a non-conent file"

To start with all of our models work in a standard windows monogame project. In fact the game we are porting is “Hydraulic Empire” on steam.

In the process of porting the game over to a windows universal app we can not get any of our skinned models to load (tried quite a few of them) and it comes back with the “could not load asset as a non-conent file”. Everything else we have tried loads, all our 2d assets, and all our non skinned models.

Is there something I am missing here? Is it not possible?

For more info. I did check that they were marked as content files, and they are in the proper locations. I also made sure that all their textures are in the correct place (including the _0 ones). Everything that I can think of, I/we have checked…