title: The argument prompt can not be converted to type String
body: <p>My Code:</p>
  
  <pre><code>con.Open()
  cmd = New SqlCommand("select max(LID) from Lieferanten", con)
  Dim newIDSupplier As Double = cmd.ExecuteScalar
  newIDSupplier += 1
  con.Close()
  
  con.Open()
  cmd = New SqlCommand("INSERT into LIEFERANTEN(LID, LNAME1) VALUES(@newIDSupplier, @companyName)", con)
  cmd.Parameters.AddWithValue("@newIDSupplier", newIDSupplier)
  
  cmd.ExecuteNonQuery()
  con.Close()
  </code></pre>
  
  <p>At <code>cmd.ExecuteNonQuery()</code> always comes the error message:</p>
  
  <blockquote>
    <p>The argument prompt can not be converted to type String</p>
  </blockquote>
  
  <p><a href="https://i.stack.imgur.com/HMseF.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/HMseF.jpg" alt="Error"></a></p>
  
  <p>Any help is apprecated.</p>