If cobbys feature to create a new API User in Magentos Backend keeps failing, you can try to create a new API User without our feature, by hand.
The way to make a new API-User 'by hand' is as follows:
Then check the API-Role 'cobby' if the user is now part of it
9. Click on the role 'cobby'
13. Go to System -> Configuration -> Services / cobby and enter the new users name under User Name and his password under API-KEY.
14. Click "Save Config"