how-to-npm: 03 login : unable to create new user

Trying to go through 03 login but unable to add a user with the adduser command.

This is the message i get in my npm-debug file:

0 info it worked if it ends with ok
1 verbose cli [ '/home/ubuntu/.nvm/versions/node/v4.1.1/bin/node',
1 verbose cli   '/home/ubuntu/.nvm/versions/node/v4.1.1/bin/npm',
1 verbose cli   'whoami' ]
2 info using npm@3.5.3
3 info using node@v4.1.1
4 verbose stack Error: this command requires you to be logged in.
4 verbose stack     at EventEmitter.whoami (/home/ubuntu/.nvm/versions/node/v4.1.1/lib/node_modules/npm/lib/whoami.js:41:18)
4 verbose stack     at Object.commandCache.(anonymous function) (/home/ubuntu/.nvm/versions/node/v4.1.1/lib/node_modules/npm/lib/npm.js:216:13)
4 verbose stack     at EventEmitter.<anonymous> (/home/ubuntu/.nvm/versions/node/v4.1.1/lib/node_modules/npm/bin/npm-cli.js:74:30)
4 verbose stack     at doNTCallback0 (node.js:407:9)
4 verbose stack     at process._tickCallback (node.js:336:13)
5 verbose cwd /home/ubuntu/workspace
6 error Linux 4.2.0-c9
7 error argv "/home/ubuntu/.nvm/versions/node/v4.1.1/bin/node" "/home/ubuntu/.nvm/versions/node/v4.1.1/bin/npm" "whoami"
8 error node v4.1.1
9 error npm  v3.5.3
10 error code ENEEDAUTH
11 error need auth this command requires you to be logged in.
12 error need auth You need to authorize this machine using `npm adduser`
13 verbose exit [ 1, true ]

and this is what i get after trying to add a user:

yannhulot:~/workspace/ProjectFolder $ npm adduser
Username: yann
Password: 
Email: (this IS public) yann@pc.com
npm ERR! Linux 4.2.0-c9
npm ERR! argv "/home/ubuntu/.nvm/versions/node/v4.1.1/bin/node" "/home/ubuntu/.nvm/versions/node/v4.1.1/bin/npm" "adduser"
npm ERR! node v4.1.1
npm ERR! npm  v3.5.3
npm ERR! code E400

npm ERR! Unknown error while authenticating : -/user/org.couchdb.user:yann
npm ERR! 
npm ERR! If you need help, you may report this error at:
npm ERR!     <https://github.com/npm/npm/issues>

npm ERR! Please include the following file with any support request:
npm ERR!     /home/ubuntu/workspace/ProjectFolder/npm-debug.log
yannhulot:~/workspace/ProjectFolder $ 

Any help on how to solve the problem would be appreciated. Thanks.