Following this answer I am able to connect to an IIS Express instance with debugging.
However, I am only able to place breakpoints in a small set of my ASP pages, as shown in the VS2012 Solution Explorer while the debugger is attached to the website's IIS Express process:
These are basically the first ~20 ASP files in the site's directory hierarchy.
If I try to put a breakpoint in any other ASP file in the solution I get a tooltip message:
The breakpoint will not currently be hit. No symbols have been loaded for this document.
How do can I enable breakpoint debugging in all ASP files in the website?