You need to define the namespace called 'local'.

For example, the namespace named 'local' below is defined as Iridyn.Facilitator:

Code:
 
<UserControl x:Class="Iridyn.Facilitator.Controls.ScheduleExplorerControl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:Iridyn.Facilitator"
VerticalAlignment="Stretch" >
<UserControl.Resources>
<HierarchicalDataTemplate DataType="{x:Type local:ExplorerNode}"
ItemsSource="{Binding Path=ChildNodes}">
<Grid>
 ....
</Grid>
</HierarchicalDataTemplate> 
</UserControl.Resources>