(I posted this in the Silverlight Programming with .NET forum)

FYI. I ran into this problem tonight, and thought I'd post the solution here.

I am using sample controls in the SDK. In my solution, I have kept the 1.1 SDK example in its own project, as it is shipped, and I reference it from my main project.

In the Silverlight SDK Controls examples, there is a class named ControlBase. In my main project, I have a button-type control that inherits from SDK ButtonBase which inherits from ControlBase.

The SDK ControlBase constructor tries to be clever about picking up the name of the xaml file that contains the markup for the derived control. Unfortunately, it is unable to check outside of its own assembly because it calls this code:

     Assembly assembly = typeof(ControlBase).Assembly;
     string[] names = assembly.GetManifestResourceNames();

which brings back only xaml files that are part of the SL Samples assembly.Changing that line to this fixes the problem:

     Assembly assembly = this.GetType().Assembly;
     string[] names = assembly.GetManifestResourceNames();