Trigger usercontrol storyboard from inner contentcontrol in wpf - wpf

Question

I have two usercontrols:
Usercontrol 1:
- contains a storyboard animation in the usercontrol resources named "somestoryboard".
- contains a keyboard that has to be slide up when someone clicks on a textbox in usercontrol 2.
- contains a contentcontrol where any usercontrol dynamically resides.
Usercontrol 2:
- Contains a textbox with an eventtrigger. When touched the storyboard from usercontrol 1 has to be fired.
Unfortunately the whole binding goes wrong in the second user control. I constantly get the message "couldn't find object of storyboard".
How do I set this binding right in usercontrol 2, or is this even possible in purely xaml?
Here are the two usercontrols:
Usercontrol 1:
<UserControl (some namespaces)>
<UserControl.Resources>
<Storyboard x:Key="SomeControl">
<BooleanAnimationUsingKeyFrames Storyboard.TargetName="aControl"
Storyboard.TargetProperty="Expanded" >
<DiscreteBooleanKeyFrame Value="True" KeyTime="0:0:0" />
</BooleanAnimationUsingKeyFrames>
</Storyboard>
</UserControl.Resources>
<Grid>
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition Height="500" />
<RowDefinition />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition Width="800" />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<Grid Grid.Column="1" Grid.Row="1" Background="{StaticResource DefaultBackground}" >
<Grid.ColumnDefinitions>
<ColumnDefinition Width="100" />
<ColumnDefinition />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="100"/>
<RowDefinition />
<RowDefinition Height="70" />
</Grid.RowDefinitions>
<ContentControl Grid.Row="1" Grid.Column="2" Margin="10,0,20,0" VerticalContentAlignment="Top"/>
</Grid>
<Controls:Somecontrol x:Name="aControl" VerticalAlignment="Bottom" Height="0" HorizontalAlignment="Stretch"
Grid.Column="0" Grid.ColumnSpan="3" Grid.Row="1" Grid.RowSpan="2" UseAnimation="True"
Style="{StaticResource AnimatedControl}" />
</Grid>
Usercontrol 2:
<UserControl (some namespaces)>
<Grid Margin="5" >
<Grid.RowDefinitions>
<RowDefinition Height="auto" />
<RowDefinition Height="auto"/>
</Grid.RowDefinitions>
<TextBox Grid.Row="0" Text="{Binding InputMessage}" VerticalAlignment="Center" FontSize="12" Margin="0,0,0,5" />
<TextBox Grid.Row="1" Text="{Binding InputResult}" InnerBorderBrush="Blue" CornerRadius="5" Background="White" >
<TextBox .Triggers>
<EventTrigger RoutedEvent="TextBox.TouchUp">
<BeginStoryboard Storyboard="{StaticResource SomeControl}" />
</EventTrigger>
</TextBox.Triggers>
</TextBlock >
</Grid>
</UserControl>