XAML editor just keeps showing: The member is not recognized or is not accessible
<p>I created an UserControl: A TextBox that shows an icon on the left side. My code seems to work but the following error keeps showing and makes the XAML editor mark it as an error.</p>

<blockquote>
  <p>The member is not recognized or is not accessible.</p>
</blockquote>

<p>I also don't get autocompletion inside my properties at all, I assume it is because of the error? I'm not that familiar with WPF UserControls.</p>

<p>I have already cleaned and rebuilt / restarted my project multiple times. That didn't help, the XAML editor just keeps showing this error on every custom property.</p>

<p>I'm using .NET 4.6.1.</p>

<p>LoginWindow.xaml:</p>

<pre><code>&lt;Window x:Class="SMSBrowser.LoginWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:control="clr-namespace:SMSBrowser.Controls"
    Title="SMS Browser - Login" SizeToContent="WidthAndHeight" ResizeMode="NoResize" Background="DimGray"&gt;
&lt;Grid&gt;
    &lt;StackPanel Margin="30" HorizontalAlignment="Center" VerticalAlignment="Center"&gt;
        &lt;TextBlock Text="Test" TextAlignment="Center" FontSize="32" FontWeight="Bold" Foreground="White" Margin="0,0,0,25" /&gt;
        &lt;control:IconTextBox CustomBackground="Yellow" CustomIconSource="..\Resources\Icons\User.ico" Height="25" Margin="0,0,0,4" /&gt;
        &lt;control:IconTextBox CustomBackground="Red" CustomIconSource="..\Resources\Icons\Key.ico" Height="25" Margin="0,4,0,4" /&gt;
        &lt;Button Content="Login" Height="25" Width="400" Margin="0,4,0,0" /&gt;
    &lt;/StackPanel&gt;
&lt;/Grid&gt;
</code></pre>

<p></p>

<p>IconTextBox.xaml</p>

<pre><code>&lt;UserControl x:Class="SMSBrowser.Controls.IconTextBox"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
         mc:Ignorable="d"
         d:DesignHeight="25" d:DesignWidth="300"
         x:Name="LayoutRoot"&gt;
&lt;Border BorderBrush="{Binding Path=CustomBorderBrush, ElementName=LayoutRoot}" BorderThickness="{Binding Path=CustomBorderThickness, ElementName=LayoutRoot}"&gt;
    &lt;DockPanel Background="{Binding Path=CustomBackground, ElementName=LayoutRoot}"&gt;
        &lt;Image Source="{Binding Path=CustomIconSource, ElementName=LayoutRoot}" Margin="{Binding Path=CustomIconMargin, ElementName=LayoutRoot}" DockPanel.Dock="Left" /&gt;
        &lt;TextBox Text="{Binding Path=CustomText, ElementName=LayoutRoot}" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" VerticalContentAlignment="Center" BorderThickness="0" /&gt;
    &lt;/DockPanel&gt;
&lt;/Border&gt;
</code></pre>

<p></p>

<p>IconTextBox.cs</p>

<pre><code>namespace SMSBrowser.Controls
{
/// &lt;summary&gt;
/// Interaction logic for IconTextBox.xaml
/// &lt;/summary&gt;
public partial class IconTextBox : UserControl
{
    public IconTextBox()
    {
        InitializeComponent();
        DataContext = LayoutRoot;
    }

    public string CustomBackground
    {
        get { return (string)GetValue(CustomBackgroundProperty); }
        set { SetValue(CustomBackgroundProperty, value); }
    }

    public static readonly DependencyProperty CustomBackgroundProperty =
        DependencyProperty.Register("CustomBackground", typeof(string), typeof(IconTextBox));

    public string CustomBorderBrush
    {
        get { return (string)GetValue(CustomBorderBrushProperty); }
        set { SetValue(CustomBorderBrushProperty, value); }
    }

    public static readonly DependencyProperty CustomBorderBrushProperty =
        DependencyProperty.Register("CustomBorderBrush", typeof(string), typeof(IconTextBox), new PropertyMetadata(""));

    public string CustomBorderThickness
    {
        get { return (string)GetValue(CustomBorderThicknessProperty); }
        set { SetValue(CustomBorderThicknessProperty, value); }
    }

    public static readonly DependencyProperty CustomBorderThicknessProperty =
        DependencyProperty.Register("CustomBorderThickness", typeof(string), typeof(IconTextBox), new PropertyMetadata(""));

    public string CustomIconMargin
    {
        get { return (string)GetValue(CustomIconMarginProperty); }
        set { SetValue(CustomIconMarginProperty, value); }
    }

    public static readonly DependencyProperty CustomIconMarginProperty =
        DependencyProperty.Register("CustomIconMargin", typeof(string), typeof(IconTextBox), new PropertyMetadata(""));

    public string CustomIconSource
    {
        get { return (string)GetValue(CustomIconSourceProperty); }
        set { SetValue(CustomIconSourceProperty, value); }
    }

    public static readonly DependencyProperty CustomIconSourceProperty =
        DependencyProperty.Register("CustomIconSource", typeof(string), typeof(IconTextBox), new PropertyMetadata(""));

    public string CustomText
    {
        get { return (string)GetValue(CustomTextProperty); }
        set { SetValue(CustomTextProperty, value); }
    }

    public static readonly DependencyProperty CustomTextProperty =
        DependencyProperty.Register("CustomText", typeof(string), typeof(IconTextBox), new PropertyMetadata(""));
}
}
</code></pre>

<p>Screenshot:</p>

<p><a href="https://i.stack.imgur.com/cQqx1.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cQqx1.png" alt="Errors"></a></p>