Custom elements on canvas

Question

I am trying to write a custom element onto a canvas with the following code:

<UserControl x:Class="SketchPuzzle.Content.MenuScreen.View.MenuScreenView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:Custom="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
    xmlns:ignore="http://www.ignore.com"
    xmlns:mccce="clr-namespace:MvvmControlChange.Content.Elements;assembly=MvvmControlChange"

[...]

<Canvas Name="Page_2" Width="1200" Height="900" >

            <mccce:Line_Element 

            x:Name="l1" 
            Width="500" 
            Height="200" 
            x:Uid="content" 
            Canvas.Left="143" 
            Canvas.Top="98" 
            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

            </mccce:Line_Element>
        </Canvas>

I get the Message that "Line_Element is not usable as an object element because it is not public or does not define a public parameterless constructor or a type converter."

The element IS public, has the following constructor

public Line_Element(int x, int y, string id){...}

and i cant tell what a type converter is. What am i doing wrong?