Cannot create an instance of "[user control]" error in designer

Question

I have created the following user control. When I add it to a xaml window, I get the error "Cannot create an instance of "ucAppItem". I dragged the user control onto the window from the toolbar.

XAML of user control is as follows:

<UserControl x:Class="Demos.ucAppItem"
             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" Width="852" Height="215">
    <Grid>

        <Label Name="lblTitle"  Content="Title" HorizontalAlignment="Left" Margin="233,10,0,0" VerticalAlignment="Top" FontSize="22" FontFamily="Arial"/>


        <Image Width="40" Height="40" VerticalAlignment="Center" HorizontalAlignment="Right" Margin="0,0,80,0">
            <Image.Style>
                <Style TargetType="{x:Type Image}">
                    <Setter Property="Source" Value="pack://siteoforigin:,,,/arrow2.png"/>
                    <Style.Triggers>
                        <Trigger Property="IsMouseOver" Value="True">
                            <Setter Property="Source" Value="pack://siteoforigin:,,,/arrow1.png"/>
                        </Trigger>
                    </Style.Triggers>
                </Style>
            </Image.Style>
        </Image>
        <Label x:Name="lblRun" Content="Run" HorizontalAlignment="Right" Margin="0,88,35,0" VerticalAlignment="Top" Foreground="#FF2EAADC" FontSize="20">
            <Label.Style>
                <Style TargetType="{x:Type Label}">
                    <Setter Property="Foreground" Value="#FF2EAADC"/>
                    <Style.Triggers>
                        <Trigger Property="IsMouseOver" Value="True">
                            <Setter Property="Foreground" Value="#006d9e"/>
                        </Trigger>
                    </Style.Triggers>
                </Style>
            </Label.Style>
        </Label>
    </Grid>
</UserControl>

XAML of window is as follows:

<Window
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:Demos" x:Class="Demos.Window1"
        Title="Window1" Height="487" Width="854">
    <Grid>

        <local:ucAppItem/>

    </Grid>
</Window>

Thanks for your help in advance!

Answer 1

@Anatoily Nikolaev - thanks for your help! Your pointer on the label fixed the issue I had with it and you were right about the image. I'll mark your response as the answer. It was the source that was the issue.

My label is now defined as:

   <Label x:Name="lblRun" Content="Run" HorizontalAlignment="Right" Margin="0,88,35,0" VerticalAlignment="Top" FontSize="20">
        <Label.Style>
            <Style TargetType="{x:Type Label}">
                <Setter Property="Foreground" Value="#FF2EAADC"/>
                <Style.Triggers>
                    <Trigger Property="IsMouseOver" Value="True">
                        <Setter Property="Foreground" Value="#006d9e"/>
                    </Trigger>
                </Style.Triggers>
            </Style>
        </Label.Style>
    </Label>

My image is now defined as:

       <Image>
            <Image.Style>
                <Style TargetType="{x:Type Image}">
                    <Setter Property="Source" Value="{StaticResource arrow2}"/>
                    <Setter Property="Height" Value="40"/>
                    <Setter Property="Width" Value="40"/>
                    <Setter Property="VerticalAlignment" Value="Center"/>
                    <Setter Property="Margin" Value="0,0,80,0"/>
                    <Setter Property="HorizontalAlignment" Value="Right"/>
                    <Style.Triggers>
                        <Trigger Property="IsMouseOver" Value="True">
                            <Setter Property="Source" Value="{StaticResource arrow1}"/>
                        </Trigger>
                    </Style.Triggers>
                </Style>
            </Image.Style>
        </Image>

And I have resources (set in the App.xaml file), set as this:

<Application x:Class="demos.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <BitmapImage x:Key="arrow1" UriSource="arrow1.png" />
        <BitmapImage x:Key="arrow2" UriSource="arrow2.png" />
    </Application.Resources>
</Application>

Answer 2

First, instead of pack://siteoforigin:,,,/arrow2.png need to write your actual URI and to make sure that the file exists in the project as a resource, like this (MSDN):

pack://application:,,,/arrow1.png

Secondly, trigger style for the label lblRun, will not work because you set this Foreground value locally, in WPF have a list of value precedence (MSDN), that the local value of a higher priority than the trigger style:

<Label x:Name="lblRun" Foreground="#FF2EAADC" FontSize="20" ... />

Try to remove it Foreground local value and use Style setter:

<Label x:Name="lblRun" Content="Run" HorizontalAlignment="Right" Margin="0,88,35,0" VerticalAlignment="Top" FontSize="20">
    <Label.Style>
        <Style TargetType="{x:Type Label}">
            <Setter Property="Foreground" Value="#FF2EAADC"/>

            <Style.Triggers>
                <Trigger Property="IsMouseOver" Value="True">
                    <Setter Property="Foreground" Value="#006d9e"/>
                </Trigger>
            </Style.Triggers>
        </Style>
    </Label.Style>
</Label>