I figured it out. The problem was that there were still some pages in the project that hadn’t been converted to use “namespaces” as needed in a web application project. I guess I thought that it wouldn’t compile if there were still any of those pages around, but if the page didn’t reference anything from outside itself it didn’t appear to squawk. So when it was saying that it didn’t inherit from “System.Web.UI.Page” that was because it couldn’t actually find the class “BasePage” at run time because the page itself was not in the WebApplication namespace.
I went through all my pages one by one and made sure that they were properly added to the WebApplication namespace and now it not only compiles without issue, it also displays normally. yay!
what a trial converting from website to web application project can be!