Compiler Error Message: CS0115: 'ASP.pagename_aspx.GetTypeHashCode()': no suitable method found to override

I came accross this problem today when converting a set of application pages into master pages.

My initial problem was that I had set CodeFile attribute of the @Page directive, rather than the CodeBehind attribute.

The second problem was that my page was inheriting from the Masterpage, rather than from System.Web.Ui.Page.

When I fixed these it worked.

It essence, if you get this error, check out what, and where your page is inheriting from.