You can only import data into the same version that exported it. If you use 4.0.19 (or 4.0.xx for the latest 4.0) you'll get a slightly better error message.

You'll need to run Spine twice. I believe what you want is the following:

First, use 3.8.99 to import the 3.8 data into a Spine project file:

Spine -u 3.8.99 -i H:\spineC\wwww\skeleton-3.8.json -o H:\spineC\wwww\skeleton.spine 

---

import

Next, use 4.0 to export 4.0 data:

Spine -u 4.0.xx -i H:\spineC\wwww\skeleton.spine -o H:\spineC\wwww\exports 

---

export json

This uses the special `

export json` parameter, which exports using default JSON settings. Alternatively, you can specify an export settings file, see:
Command line interface - Spine User Guide: Export

Keep your project file somewhere safe so you don't need to repeat the first step in the future! Using the project file you can easily export a new JSON or binary data file, as shown in the second step above. For example, when you want to move to 4.1, you would just do:

Spine -u 4.1.xx -i H:\spineC\wwww\skeleton.spine -o H:\spineC\wwww\exports 

---

export json

Lastly, note that the input (-i) parameter for `

export` can be a folder. If you have all your project files in the same folder, you can export them all at once:

Spine -u 4.0.xx -i H:\spineC\wwww -o H:\spineC\wwww\exports 

---

export json

Otherwise you can specify multiple exports with one Spine invocation:

Spine -u 4.1.xx -i H:\spineC\wwww\skeleton1.spine -o H:\spineC\wwww\exports 

---

export json -i H:\spineC\wwww\skeleton2.spine -o H:\spineC\wwww\exports 

---

export json

Oops, I mispoke, sorry! It's `

import/-rthat can be a path to a folder. We'll make

export/-e` support a folder path in the future.