The error message explains it well. There is License class in Aspose.Word, Aspose.Spell and ComponentModel namespaces. If you just use License class, the compiled does not know which class to use hence the error. The standard way out is to use fully qualified class name (that's what the namespaces were designed for). I don't see how using full class name fails to help, maybe you have License mentioned elsewhere.
Roman Korchagin
Lead Developer,
Aspose Auckland Team