Yeah, I have the same problem. No fix yet.

I found out that the most probable error is actually the internet connection (as it was in my case). If your router blocks the upload to a certain IP address/port then all your Steam Workshop uploads will fail.

I checked, I have no locks.

If you are creating your map offline and is trying also to subscribe to workshop, don't do it. Looks like the game (or Steam) can handle this, in my case, I stick with my map saved locally and do not sub to my own map.