Expose more Greenworks Steam cloud APIs to NW.Js and Electron (1.11.0: Supports Greenworks v0.18.0 for NW.Js v0.92.0, Steamworks SDK 1.60).
Can you try again and make sure you are using 1.4.1? I just tried with 1.4.1 and it looked ok. If there is still an error, open the dev console and send the details of the error.