MVVM command on ContextMenu

I am trying to add a command to a context menu menuitem on a NodeTemplate and I am getting the following error:

System.Windows.Data Error: 40 : BindingExpression path error: 'TestValue' property not found on 'object' ''PartBinding' (HashCode=9445854)'. BindingExpression:Path=ChkSumValue; DataItem='TestValue' (HashCode=9445854); target element is 'TextBox' (Name='txtTestValue'); target property is 'Text' (type 'String').
I think the issue is I can't seem to get to the DataContext of my UserControl. It is trying to look at the PartBinding. Is there a way for me to get back to the DataContext of the Control when using the context menu on a Node template?

I found the binding I needed to get back to the DataContext of the diagram (which is the same DataContext as the UserControl). So to call a command in the VM, I just changed the binding to:

Command="{Binding Path=Part.Diagram.DataContext.SomeCommand}" CommandParameter="{Binding Path=Part.Diagram.SelectedPart}"