DoubleAnimation exception when animating grid width with DataTrigger - wpf

Question

I'm trying to animate a grid's width upon a toggle button being checked. I've used a data trigger in the Grid's style element to do this, however, whenever it's triggered I get an error, stating:
Cannot animate the 'Width' property on a
'System.Windows.Controls.Grid' using a
'System.Windows.Media.Animation.DoubleAnimation'
I'm pretty sure it is possible to animate the grid in the way I'm attempting, as I've gotten it to work using a click event. Does anyone see where I'm going wrong here?
<Grid Margin="0" HorizontalAlignment="Left"
TextOptions.TextFormattingMode="Display" x:Name="MainGrid" >
<Grid.Resources>
<Style TargetType="Grid">
<Style.Setters>
<Setter Property="Width" Value="300"/>
</Style.Setters>
<Style.Triggers>
<DataTrigger Binding="{Binding Path=IsChecked, ElementName=CollapseIcon}" Value="True">
<DataTrigger.EnterActions>
<BeginStoryboard >
<Storyboard >
<DoubleAnimation Duration="0:0:0.200" Storyboard.TargetProperty="Width" To="16" />
</Storyboard>
</BeginStoryboard>
</DataTrigger.EnterActions>
</DataTrigger>
</Style.Triggers>
</Style>
</Grid.Resources>

Answer 1

I apologize man, I completely forgot to get back to this Friday and then saw your question again today. Anyway you're so close! Move your dependency property for Width to the object and you're all done! This tested just fine on my end. Cheers!
<Window x:Class="MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Grid>
<Grid Margin="0" HorizontalAlignment="Left" Width="300" Background="Red"
TextOptions.TextFormattingMode="Display" x:Name="MainGrid" >
<Grid.Resources>
<Style TargetType="Grid">
<Style.Triggers>
<DataTrigger Binding="{Binding Path=IsChecked, ElementName=CollapseIcon}" Value="True">
<DataTrigger.EnterActions>
<BeginStoryboard >
<Storyboard >
<DoubleAnimation Duration="0:0:0.2"
Storyboard.TargetProperty="Width"
From="300" To="16" />
</Storyboard>
</BeginStoryboard>
</DataTrigger.EnterActions>
</DataTrigger>
</Style.Triggers>
</Style>
</Grid.Resources>
</Grid>
<ToggleButton x:Name="CollapseIcon" Content="Magic!" Height="50" Width="50"/>
</Grid>
</Window>
ADDENDUM: Forgot in a DoubleAnim you need to be explicit with both To AND FROM or it just returns NaN in the From by default. Cheers!