Unable to reference/bind to view template in user control - wpf

Question

I have a view template in a user control as below
<UserControl
x:Class="Configuration.Views.viewProfileTemplate"
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="300" d:DesignWidth="300">
<Grid Background="Azure" Width="233">
<StackPanel Height="300" HorizontalAlignment="Left" Name="stackPanel1" VerticalAlignment="Top" Width="230">
<TextBox Text="{Binding Path=SomeProfileText}" Margin="10" />
<ListBox ItemsSource="{Binding Path=Profiles}" Height="70" Margin="10"/>
<CheckBox Content="CheckBox" Height="16" Name="checkBox1" Width="175" />
</StackPanel>
</Grid>
</UserControl>
The user control is defined as below in the main.xaml window
<Window x:Class="Configuration.TreeUI"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:views="clr-namespace:Configuration.Views"
xmlns:local="clr-namespace:Configuration"
Title="TreeUI" Height="300" Width="450" WindowStyle="ToolWindow">
I atempt to use the template with
<DataTemplate DataType="{x:Type local:ProfileViewModel}">
<Views:viewProfileTemplate/>
</DataTemplate>
But the compiler reports :
Error 1 The type 'Views:viewProfileTemplate' was not found. Verify that you are not missing an assembly reference and that all referenced assemblies have been built.
I again am missing som important point, but what ?
Going to owe someone a big drink .....

Answer 1

There are two potential causes for this:
1) If the data template is in a different assembly than viewProfileTemplate, you need to make the xaml reflect this:
xmlns:views="clr-namespace:Configuration.Views;assembly=ViewAssembly"
Note that this will also require a reference to be added to the project properly to function.
2) If this is a design time error, make sure to build the solution first. The WPF designer in VS often will report errors about missing types until you've built once, then it "works" properly.