Catastrophic failure! Now that is an error message worthy of my college dating life!... anyhoo, I digress. Many controls in winforms and WPF probably try to do things in the constructor or an "OnLoad" event of some kind that are not design-time-friendly, but the magic of the environment mostly keeps things like this from happening. This magic dust has not yet been sprinkled upon the Silverlight 2.0 tools for VS2008, but I'm still very excited about the possibilities as this platform matures. The error below occurs if I add some test images into the loaded event of the carousel and try to view the designer.