I'm having this same issue, and have walked through the same steps as you've kindly outlined for Snorre - checked that grunt is installed, and made sure that there's a path specified for it in my environmental variables. My error message is this:

ERROR: Failed to build the web application, ('grunt' is not recognized as an internal or external command,

operable program or batch file.
)
Install will continue. Try again after installation completes using 'grunt build:prod'.

Install was unsuccessful. Please check the console output.

I've successfully installed all other components, and MongoDB is running. This seems to be the final hurdle (after many). Please help??