The .aspx pages are the only ones that support the Src attribute, and therefore it’s the only file type that supports JIT compilation of separate source files.By using the Src attribute in the page directive, you can specify which file the ASP.NET engine should compile.
It cannot be used with a WebService.
This means that you must precompile the code behind class that is to be used as the basis for the Web Service, either manually using the Command-line compiler or by building a Visual Studio.NET Web Service Application.