When I added a new Master page in Visual Studio 2005, named as MyApp.Master, the generated class was named just MyApp.
I've already have a namespace with the same name MyApp, and it caused the compiler errors.
It will be good if new file wizard by default create class names, that include the type of generated object, e.g. MyAppMaster class.
Similar should be apply for other ASP.NET objects, e.g. Customer.aspx page should use CustomerPage class, and Customer.ascx user control should use CustomerUsc class.