System.Windows.Baml2006.TypeConverterMarkupExtension threw an exception

This error has started to be thrown on one of our development machines. The following code is the cause

<Style.Triggers><Trigger Property="Validation.HasError" Value="True"><Setter Property="ToolTip"><Setter.Value><Binding Path="(Validation.Errors)[0].ErrorContent" RelativeSource="{x:Static RelativeSource.Self}" /></Setter.Value></Setter></Trigger></Style.Triggers>

 This XAML is in an ElementHost control on a Windows Form in VS2010. The code has previously worked OK and still appears to work on other machines. The solution contains multiple projects and I have deleted and reloaded the project from source code.

When the code is commented out the form loads OK (albeit without the tooltip functionality). When the code is uncommented this error returns

System.Windows.Markup.XamlParseException occurred
 Message='Provide value on 'System.Windows.Baml2006.TypeConverterMarkupExtension' threw an exception.' Line number '66' and line position '42'.
 Source=PresentationFramework
 LineNumber=66
 LinePosition=42

I have seen a few posts and related topics on similar errors without seeing any definite resolution. Has anyone encountered something like this and been able to fix it?