This thread looks to be a little on the old side and therefore may no longer be relevant. Please see if there is a newer thread on the subject and ensure you're using the most recent build of any software if your question regards a particular product. Otherwise - post away!
Using WPF Elements 18.104.22.168, the simple configuration of a DataGridWithin a StackPanel will cause an InvalidOperationException on startup:
The issue appears to be that DataGridPanel.ArrangeOverride() returns a PositiveInfinity for DesiredHeight. While it is not too difficult to alter the xaml to have some fixed height relation and avoid the error, it is rather annoying. I've attached a simple test app that illustrates the issue.