Unable to create user error: "user already exists"

Question: When I try to create a new user, I get error message "User already exists".

Answer:
This error indicates that the user account you are trying to create already exists therefore it cannot be created again. There are three possibilities of this error:

1. Anonymous user permissions problem.
2. User account exists in operating system.
3. User account exists in HC database.

Solution:
Here we will discuss these three possibilities one-by-one.

Anonymous User Permissions: Hosting Controller website must be running under its own Anonymous user and that user must be added in "Administrators" group.

To set anonymous user:

1. Open IIS Console.
2. Select Hosting Controller virtual directory Admin at Hosting Controller site. Right click on this directory and click Properties, go to Directory Security tab.
3. Click Edit button under Anonymous access and authentication control.
4. Enable the Anonymous Access check box, click Edit, click Browse and select HCAdministrator (This user is in administrative group) and click Ok.
5. Enable the check box Allow IIS to control password and click Ok.
   Note: After clicking Ok button, if you get any prompt, click Yes button.
   
6. Enable the check box Integrated Windows authentication. Clear the check box Basic authentication (password is sent in clear text) and click Ok.
   Note: After clicking Ok button, if you get any prompt, click Yes button.
   
7. Click Ok to apply changes.

User Account Exists in Operating System: HC users are created in operating system. If a user is not listed in My Users under User Manager then it should be checked for existence in operating system. If the account is present in operating system it should be removed from there.

To check account existence in operating system:    

1. Open Computer Management. To open Computer Management, follow this path Start :: Settings :: Control Panel :: Administrative Tools, and then double click Computer Management.
2. In the console tree, click Local Users and Groups. Click Users and search for user account. If account is present, delete it. 

User Account Exists in Hosting Controller Database: You can get this error if user account is already created and present in HC database.

To check the presence of user account in HC database:

1. Login into HC as "Host/Reseller". Click User Manager and then click on My Users.
2. You can perform quick and easy search for the required user account by entering the login name (user name) in the search box. Click Search icon to display the required user details, if it exists under the respective logged in level (as host/reseller) in the table view.