No luck, I have attached a screenshot which shows hopefully enough detail to solve the problem. You can see the path to the file and my code. I tried both methods.
You may have noticed the paths vary in my two code samples, that is because I have the png in both my silverlight project and my web project. I did get it working when I used an absolute URL pointing to the published project, however that is not a viable permanent solution.
I also tried variations:
Source =
new BitmapImage(new Uri("/STSilver;Images/Icons16/Clear.png", UriKind.Relative)),
Source =
new BitmapImage(new Uri("/STSilver;./Images/Icons16/Clear.png", UriKind.Relative)),
Source = new BitmapImage(new Uri("./images/menuicons/clear.png", UriKind.Relative)),
Source =
new BitmapImage(new Uri("/ST3_Source;Images/menuicons/clear.png", UriKind.Relative)),
note: Menuicons is the subfolder in my web project where the png is located.
ST3_Source is the solution and web project name.