Duplicate user name error when logging in to Web Help Desk

When you attempt to log in to Web Help Desk, the following error is displayed: 

More than one match found for <username@domain.com> in account 1

1. Verify that a duplicate account does not exist for the user. If a duplicate exists, delete or merge the account.
   1. Click Clients in the toolbar.
   2. Click the Advanced Search tab.
   3. Create a search condition based on the email or user name.
   4. Delete or merge the duplicate account. 
2. Verify that the client's email address is not used by another client account as a secondary email address. If this issue exists, remove the email account on the secondary client account.
   1. Click Clients in the toolbar.
   2. Click the Advanced Search tab.
   3. Create a search condition based on email.
   4. Delete the duplicate account.