My guess is that you need to add some parameter options to the MapPageRoute
declaration. So if you have more than one webforms page in the WebForms
directory this works well.
routes.MapPageRoute ("ReportTest",
"reports/{pagename}",
"~/WebForms/{pagename}.aspx");
PS: You may also want to have a look at the RouteExistingFiles
property of RouteCollection
An alternative would be to use
<%=Html.RouteLink("Home","Default", new {controller = "Home", action = "Index"})%>