Thank you sir.
I set a breakpoint on that line and it stops saying no source available.
I'm not sure whether it's my internet connection problem or not, but my connection is working fine.
Loading user information from Channel 9
Something went wrong getting user information from Channel 9
Loading user information from MSDN
Something went wrong getting user information from MSDN
Loading Visual Studio Achievements
Something went wrong getting the Visual Studio Achievements
Sorry I forgot to mention it. It's in App.xaml.cs
if (profile.GetNetworkConnectivityLevel() == NetworkConnectivityLevel.InternetAccess).
It shows that
'NullReferenceException' was unhandled by the user code
'Object reference not set to an instance of an object.'