401 Unauthorized when contacting ASP.NET web service from ASP.NET web application

Website:

The Web Site project is compiled on the fly. You end up with a lot more DLL files, which can be a pain. It also gives problems when you have pages or controls in one directory that need to reference pages and controls in another directory since the other directory may not be compiled into the code yet. Another problem can be in publishing.

If Visual Studio isn't told to re-use the same names constantly, it will come up with new names for the DLL files generated by pages all the time. That can lead to having several close copies of DLL files containing the same class name, which will generate plenty of errors. The Web Site project was introduced with Visual Studio 2005, but it has turned out not to be popular.

Web Application:

The Web Application Project was created as an add-in and now exists as part of SP 1 for Visual Studio 2005. The main differences are the Web Application Project was designed to work similarly to the Web projects that shipped with Visual Studio 2003. It will compile the application into a single DLL file at build time. To update the project, it must be recompiled and the DLL file published for changes to occur.

Another nice feature of the Web Application project is it's much easier to exclude files from the project view. In the Web Site project, each file that you exclude is renamed with an excluded keyword in the filename. In the Web Application Project, the project just keeps track of which files to include/exclude from the project view without renaming them, making things much tidier.

Reference

The article ASP.NET 2.0 - Web Site vs Web Application project also gives reasons on why to use one and not the other. Here is an excerpt of it:

• You need to migrate large Visual Studio .NET 2003 applications to VS 2005? use the Web Application project.
• You want to open and edit any directory as a Web project without creating a project file? use Web Site project.
• You need to add pre-build and post-build steps during compilation? use Web Application project.
• You need to build a Web application using multiple Web projects? use the Web Application project.
• You want to generate one assembly for each page? use the Web Site project.
• You prefer dynamic compilation and working on pages without building entire site on each page view? use Web Site project.
• You prefer single-page code model to code-behind model? use Web Site project.

Web Application Projects versus Web Site Projects (MSDN) explains the differences between the web site and web application projects. Also, it discusses the configuration to be made in Visual Studio.

Webservices are SOAP messages (the SOAP protocol uses XML to pass messages back and forth), so your server on both ends must understand SOAP and whatever extensions you want to talk about between them, and they probably (but don't have to) be able to grok WMDL files (that "explains" the various services endpoints and remote functionality available). Usually we call this the SOAP / WS-* stack, with emphasis on 'stack' as there's a few bits of software that needs to be available, and the more complex the SOAP calls, the more of this stack needs to be available and maintained.

Using POST, on the other hand, is mostly associated with RESTful behaviours, and as an example of a protocol of such, look to HTTP. Inside the POST you can of course post complex XML, but people tend to use plain POST to simplify the calling, and use HTTP responses as replies. You don't need any extra software, probably, as most if not all webkits has got HTTP support. My own bias leans towards REST, in case you wonder. Through using HATEOAS you can create really good infrastructure for self-aware systems that can modify themselves with load and availability in real-time as opposed to the SOAP way, and this lies at the centre of the argument for it; HTTP was designed for large distributed networks in mind, dealing with performance and stability. SOAP tends to be a one-stop if-it-breaks-you're-stuffed kinda thing. (Again, remeber my bias. I've written about this a lot on my blog, especially the architecture side and the impact of SOA vs. ROA. :)

There's a great debate as to which is "better", to which I can only say "it depends completely on what you want to do, how you prefer to do it, what you need it to do, your environment, your experience, the position of the sun and the moon(s), and the mood my cat is in." Eh, meaning, a lot.

I'm all for a healthy debate about this, but I tend to think that SOAP is a reinvention; SOAP is an envelope with a header and body, and if that sounds familiar, it is exactly how HTML was designed, a fact very few people tend to see. HTTP as just a protocol for shifting stuff around is well understood and extremely well supported, and SOAP uses it to shift their XML envelopes around. Is there a real difference between shifting SOAP and HTML around? Well, yes, the big difference is that SOAP reinvents all the niceties of HTTP (caching, addressability, state, scaling), and then use HTTP only for delivering the message and nothing else and let the stack itself have to deal with those niceities mentioned earlier. So, a lot of the goodness of HTTP is ignored and recreated in another layer (hence, you need a SOAP stack to deal with it), which to me seems wasteful, ignorant and adding complexity.

Next up is what you want to do. For really complex things, there's lots in the webservices stack of standards (I think it's about 1200 pages combined these days) that could help you out, but if your needs are more modest (ie. not that crazy about seriously complex security, for example) a simple POST (or GET) of a request and an envelope back with results might be good enough. Results in HTTP is, as you probably know, HTTP content-type, so lots is already supported but you can create your own, for example application/xml+myformat (or more correctly, application/x-xml+myformat if I remember correctly). Get the request, if it's a response code 200, and parse.

Both will work. One is heavy (WS-* stack) depending on what your needs are, the other is more lightweight and already supported. The rest is glue, as they say.