The POP3 service could not create the mailbox – the account already exists

In Windows Server 2003, I have configured POP 3 service, created domains and mailboxes.
I have created many users and associate mail boxes in the POP3 service and deleted for some reasons.
When I try to create the same user I have got the error:
The POP3 service could not create the mailbox - The account already exists

Even on manually deleting the folders (mailboxes created for each user created), I got this error.
Then I came to know that the user associated with the mailbox is not deleted.
Right Click on My Computer -> Manage -> Administrative Tools -> Computer Management -> System Tools -> Local Users and groups -> Users -> Delete the user account for which you are unable to create the mailbox.
Note: Check the user associated with any other applications or any services before deleting the user.
Now, try creating the mailbox, you will be able to create the mailbox successfully!