[cdase]

I was struggling with this issue when trying to create a simple 2D geometry in Fusion 360 and importing geometry as step into Workbench, then attempting to edit in Meshing. I found several threads related to the issue, but none of them helped me solve my problem. Just wanted to post what I've found here that may be helpful even with other CAD tools. But perhaps this is just an issue related to Fusion.

This is what I did at first that wasn't working:
1. I started with a 3D solid model in Fusion.
2. I split the bodies along an arbitrary plane that I wanted to focus on in a 2D simulation.
3. I went into Patch mode and created patch surfaces of the body faces at the split. You could also do this in sculpt mode, but the resulting surfaces would be T-spline surfaces and not bodies. Patch mode creates bodies. I knew that the Meshing tool is only looking for bodies. Fusion doesn't export T-spline to step.
4. Since my new surface bodies were not in the XY plane, I did an alignment of the surface bodies to the XY plane.
5. Seems like I'm good to go at this point, so I export to step.
6. Open Workbench. Drop a geometry component. Set 2D mode in properties. Import the step file to the geometry. Drop in a mesh component attached to the geometry. Attempt to edit in meshing. Errors (see thread title).

I did several experiments, basically starting from scratch with creating various circles in a fusion sketch on the XY plane and using Patch mode to create surface bodies from those sketches. This worked just fine and Meshing was able to find all the surfaces. Then I did a move operation (in Fusion) on one of the surface bodies. I did a translate only in the XY plane. As far as I could tell there was still no Z component to the body. However, this caused Meshing to not find that surface. But it still found the surfaces that I did not move, and no errors were reported.

Here is a summary of things I found trying to get Fusion 360 2D geometry into Meshing 2D:
1. Trying to start with 3D geometry, splitting, patching, moving to XY plane, etc., didn't work. Even if I split the 3D bodies using the XY plane, still didn't work.
2. Tried creating a T-spline surface in Sculpt mode directly on the XY plane. Then converted T-spline surface to "Brep" surface body. I didn't move it at all. This didn't work either.
3. Tried creating a solid body, like a simple cylinder, having a face on the XY plane. Figured maybe Meshing would find the circular surface on the XY. Didn't work - not surprised.
4. Pretty much have to start from scratch. Create a sketch on XY plane. Create surface bodies from enclosed sketch lines in Patch mode. Do not move the surfaces, even if still constrained to XY plane. Do not rotate or align to XY plane. Do not convert from T-spline to surface body. Good to go.
5. As long as Meshing finds at least one body on the XY plane, it will be happy and report no errors. Any other bodies just won't show up.
6. Perhaps other exported file types would handle this better, but I didn't experiment. Not sure if I am missing a setting somewhere in Fusion step export.