WHMCS create new account with wrong username

When customer create a new account in WHMCS the create module is showing a error, and the user created in Wordpress USer is the same of last one....

All sites it´s getting the same username for the account. But in WHMCS the username is a new one....

Please could you have a look at images:
http://linknacional.com.br/download/

thanks
Davi