When you create a virtual machine instance for Linux images on Windows Azure you have the ability to select the user name to provision.
Linux defines a set of user names that you can't use. It is very important that you avoid using these names. If you do use one of these user names, you won't be able to provision the image.
In addition, the Service Management API will return an error that states: Failed to create user xxxxxx. This will also be true if you use a user name that already exists in the image as a result of a previous capture operation that did not deprovision the user name already created in the image.
Following are the user names that you can't use.