title: Magento : Item (Mage_Customer_Model_Customer) with the same id “####” already exist
body: <p>I have a issue here on <code>Magento</code>. </p>
  
  <p>When I tried to add a customer in <code>Mangeto admin</code> side it is giving error something like </p>
  
  <blockquote>
    <p>Item (Mage_Customer_Model_Customer) with the same id "14" already exist"</p>
  </blockquote>
  
  <p>I am adding customer with Store Id selected as <code>Admin</code> store.</p>
  
  <p>My <code>Magento</code> current version is <code>1.9.1</code></p>
  
  <p>Please advise!</p>