I love the Marmoset baker but I've ran into this problem multiple times and would love to find a solution for it. I can't remember if I solved it the last time or if I just baked it with another software. Anyway the problem is with some meshes Marmoset crashes when adding the mesh to the lowpoly folder in the baker and then selecting the folder.
I've checked if the mesh had any non-manifold issues, triangulated it, exported it as an obj and exported it from a new scene in maya but nothing have worked.
I've attached the mesh itself so you could check it out yourself if you don't know the solution from the get go! https://www.dropbox.com/sh/81syv85h3zjeubt/AAAOFwqiqD8uK2Jq6NC7k14Sa?dl=0