Fill up description field of vm through VCO with Notes?

I've read in several posts it should be possible to give in a description using the notes (or __Notes)  property

However if I try to do this from within VCO during the install of a vm using

var updateProperties = new Properties();

updateProperties.put("Notes", "Your new description field here");

I get the error "Unknown field"

What am I missing or doing wrong.

Thanks in advance