At some point in one’s Silverlight development experience, inevitably they run into a complete inability to debug their Silverlight application. While debugging you may see a breakpoint that looks like this:
The open circle indicates the breakpoint could not be set for some reason.
This just means that while your application is running successfully, Visual Studio hasn’t loaded any debugging symbols. But you hit F5 right? Why wouldn’t Visual Studio debug properly? Check the properties web project hosting your Silverlight application. It’s likely that Silverlight debugging has been turned off (or wasn’t turned on at all).