I haven't tried 2.7 yet, but I sometimes get that and just have to close the cmd window and start it up again. The first time it seems to fire up the service. There are othr ways to set up nodejs so you wont have to do it 2x. Check out some of my blogs for other tips, if you haven't already ... main one /blogs/myAlaskaGIS/2016/03/09/web-appbuilder-developer-edition-customization-resource-list?sr=search... and there are links to the others.
