To wrap text in the label control, change the the template of label as follows:
<Style x:Key="ErrorBoxStyle" TargetType="{x:Type Label}">
<Setter Property="BorderBrush" Value="#FFF08A73"/>
<Setter Property="BorderThickness" Value="1"/>
<Setter Property="Foreground" Value="Red"/>
<Setter Property="Background" Value="#FFFFE3DF"/>
<Setter Property="FontWeight" Value="Bold"/>
<Setter Property="Padding" Value="5"/>
<Setter Property="HorizontalContentAlignment" Value="Left"/>
<Setter Property="VerticalContentAlignment" Value="Top"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Label}">
<Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Padding="{TemplateBinding Padding}" SnapsToDevicePixels="true" CornerRadius="5" HorizontalAlignment="Stretch">
<TextBlock TextWrapping="Wrap" Text="{TemplateBinding Content}"/>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>