Niner since 2012
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.
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.'