It is crashing because it requires that control to be there. When you change the PanoramaItem it attempts to work with the TitleLayer
but it is null, so it throws an exception.
Instead of removing the PanningTitleLayer control, just set it's visibility to Collapsed.
<Primitives:PanningTitleLayer x:Name="TitleLayer" CharacterSpacing="-35"
ContentTemplate="{TemplateBinding TitleTemplate}" Content="{TemplateBinding Title}"
FontSize="170" FontFamily="{StaticResource PhoneFontFamilyLight}"
HorizontalAlignment="Left" Margin="10,-34,0,0" Grid.Row="0"
Visibility="Collapsed"/>