If you have
a problem with the new ContextMenu control when toggling the IsEnabled property of a MenuItem directly, take a look at this post of David Anson in which he suggests some easy workarounds.
A few days ago, Martin Naughton and Tiago Halm de Carvalho e Branco independently contacted me to report a problem they were having with the new ContextMenu control in the April '10 release of the Silverlight Toolkit. In both cases, they were toggling the IsEnabled property of a MenuItem directly and reported that the control's visuals weren't updating correctly. I was a little surprised at first because I knew I'd tested dynamic changes to the enabled state and I'd seen them work properly. But once I created a test project to investigate the report, I saw how the problem scenario was different.