Can you tell us the name and the type of asset which is involved (pkfx, meshes)
I think "OutputPath" is a field that doesn't exist anymore, and you are trying to bake an old resource ( compared to the editor version you are using to bake it )
If it's the case, normally the upgrader should remove it from the file.
You can open the asset in text-mode and manually remove the line :
OutputPath = "Something";
Hope that helps.