title: error while inserting primary key
body: <p>I'm trying (SQL Server Compact) to add primary key constraint on existing table that has some rows in it. While adding primary key I'm getting the error:</p>
  
  <blockquote>
    <p>"A duplicate key cannot be inserted into a unique index"</p>
  </blockquote>
  
  <p>I don't what this is, can anyone help me with this?</p>