ResourceDictionary is not a generic type, hence the above error makes no sense. Still, you can encounter it in a WPF project if certain conditions are met. The post describes these conditions and suggests the workarounds I know of to get rid of this bogus error message.
After I set up multiple different configurations for my ASP.NET project with different .config file transformations for different environments, a build error started showing up every time I changed to a different configuration. The issue could be resolved by manually deleting a file from obj folder, but I soon got tired of this and decided to investigate further.
Portable class libraries have recently become so ubiquitous, that it's easy to forget they don't exist all that long. As long as you're using Visual Studio 2012 or later and targeting .NET 4.5, this is not really important. But once you start targeting .NET 4, you should better keep that in mind.