Set up application resources from code

I think you need to specified the name of the component were the resource is sitting in

<ResourceDictionary Source="/<YourDllName>;component/Resources/Styles/Shared.xaml" />

If your dll is named My.Wpf.Component.dll you should put My.Wpf.Component

so in code it should be

Application.Current.Resources.MergedDictionaries.Add(new ResourceDictionary { Source = new Uri(@"/<YourDllName>;component/Resources/Styles/Shared.xaml", UriKind.Relative) });

This code works for me. I just changed the URIs to relative:

ResourceDictionary myResourceDictionary = new ResourceDictionary();

myResourceDictionary.Source = new Uri("Dictionary1.xaml", UriKind.Relative);
Application.Current.Resources.MergedDictionaries.Add(myResourceDictionary);

myResourceDictionary.Source = new Uri("Dictionary2.xaml", UriKind.Relative);
Application.Current.Resources.MergedDictionaries.Add(myResourceDictionary);