All requests to ASP.NET Web API return 404 error

I have an ASP.NET MVC 4 web site that includes Web API. The site is developed and tested with Visual Studio 2012 and .NET 4.5 on Windows 8 with IIS Express as web server. **In this development environment everything works.**

Now it is deployed on a Windows 2008 R2 (SP1) Server with IIS 7.5. .NET 4.0 and 4.5 are installed. The application pool is running with .NET 4.0 in integrated pipeline mode.

**In this production environment the MVC web site works, Web API does not.** For every request, no matter if GET or POST I get a 404 error. If I just enter a Web API Url in the browser (IE 9 opened locally on the server) to run a GET request I get a 404 page. If I issue a POST request from a Web API client application I get a 404 as well and the message:

> No HTTP resource was found that matches the request URI

**I've created a test website with MVC 4 and Web API as well and deployed it on the same server and the Web API works.** Web API and MVC assemblies have the same version number in both projects.

Furthermore I have added the [Web API Route Debugger][1] to the application. If I use a valid route like `http://myserver/api/order/12` I get the following result:

![Route Debugger][2]

For me this means that the correct route template `Api/{Controller}/{Id}` has been found and correctly parsed into a controller `Order` and `Id=12`. The controller (derived from `ApiController`) exists in the web assembly where also all MVC controllers are.

However, I don't know what the status `000` could mean and why there is no "Route selecting" section displayed (which is normally the case even if the assembly doesn't contain a single `ApiController`, see screenshots on the linked page above). Somehow it looks like no `ApiController` is found or even not searched for or the search fails silently.

The IIS log files don't show anything useful. Changing various application pool settings and using the same app pool for the test and the real application didn't help.

I am currently in the process to remove "features", configuration settings, third party assemblies, etc. from the application to bring it down to the small size of the test application in the end and hoping that at some point it starts to work.

Does somebody have a clue what the issue could be? Also any debugging or logging idea to possibly find the reason is very welcome.

**Edit**

Thanks to Darrel Miller's tip in the comments below I have integrated [Tracing for ASP.NET Web Api][3].

For the (GET) request URL `http://myserver/api/order/12` I get the following:

- **In development environment, successful** (in short form):

> Message: `http://localhost:50020/api/order/12`; Category:
> System.Web.Http.Request
>
> **Controller selection and instantiation...**
>
> Operator: DefaultHttpControllerSelector; Operation: SelectController;
> Message: Route="controller:order,id:12"; Category:
> System.Web.Http.Controllers
>
> Operator: DefaultHttpControllerSelector; Operation: SelectController;
> Message: Order; Category: System.Web.Http.Controllers
>
> Operator: HttpControllerDescriptor; Operation: CreateController;
> Message: ; Category: System.Web.Http.Controllers
>
> Operator: DefaultHttpControllerActivator; Operation: Create; Message:
> ; Category: System.Web.Http.Controllers
>
> Operator: DefaultHttpControllerActivator; Operation: Create; Message:
> MyApplication.ApiControllers.OrderController; Category:
> System.Web.Http.Controllers
>
> **Action selection, parameter binding and action invocation follows...**
>
> **Content negotiation and formatting for result...**
>
> Operator: DefaultContentNegotiator; Operation: Negotiate; Message: Typ = "String" ...
> *more*
>
> **Disposing the controller...**
>
> Operator: OrderController; Operation: Dispose; Message: ; Category:
> System.Web.Http.Controllers


- **In production environment, not successful** (in short form):

> Message: `http://myserver/api/order/12`; Category:
> System.Web.Http.Request
>
> Operator: DefaultHttpControllerSelector; Operation: SelectController;
> Message: Route="controller:order,id:12"; Category:
> System.Web.Http.Controllers
>
> **The whole part of controller activation, action selection, parameter binding, action invocation is missing and it follows content
> negotiation and formatting for the error message immediately**:
>
> Operator: DefaultContentNegotiator; Operation: Negotiate; Message:
> Type = "HttpError" ... *more*


[1]:

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[2]:

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Thanks to [Kiran Challa's][1] comment and source code from [this answer][2] I was able to figure out that an assembly (the `ReportViewer 11 assembly` for SQL Server Reporting Services) was missing on the production server.

Although no `ApiController` is in this assembly it seems to cause that controllers in assemblies - in this case my Web project's assembly - that are referencing the missing assembly are not found.

Apparently this behaviour is related to this piece of code from the [Web API's `DefaultHttpControllerTypeResolver`][3] source:

List<Type> result = new List<Type>();

// Go through all assemblies referenced by the application
// and search for types matching a predicate
ICollection<Assembly> assemblies = assembliesResolver.GetAssemblies();
foreach (Assembly assembly in assemblies)
{
Type[] exportedTypes = null;
if (assembly == null || assembly.IsDynamic)
{
// can't call GetExportedTypes on a dynamic assembly
continue;
}

try
{
exportedTypes = assembly.GetExportedTypes();
}
catch (ReflectionTypeLoadException ex)
{
exportedTypes = ex.Types;
}
catch
{
// We deliberately ignore all exceptions when building the cache. If
// a controller type is not found then we will respond later with a 404.
// However, until then we don't know whether an exception at all will
// have an impact on finding a controller.
continue;
}

if (exportedTypes != null)
{
result.AddRange(exportedTypes.Where(x => IsControllerTypePredicate(x)));
}
}

I don't know if it has to be this way and I am not quite convinced by the comment in the code but this `catch ... continue` block is rather silent about a possible problem and it took me a huge amount of time and frustration to find it. I even knew that the `ReportViewer` wasn't installed yet. I tried to install it and dependent assemblies but it was blocked by another running process on the server, so I decided to postpone the installation until I could contact the administrator and focus on MVC and WebAPI testing first - big mistake! Without Kiran's debugging code snippet I had never had the idea that the existence of a `ReportViewer.dll` could have anything to do with controller type resolution.

In my opinion there is room for improvement for the average developer like me who doesn't have a deeper knowledge about the inner workings of Web API.

After installing the missing `ReportViewer.dll` the problem disappeared.

Here are questions about the same symptom which *might have* the same reason:

-

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-

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-

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**Edit**

I have issued a request for improvement on CodePlex:

[To see links please register here]

**Edit 2 (Aug 11 '13)**

The issue has been fixed for WebAPI v5.0 RC. See the link above to the workitem and its comments section for details.


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[2]:

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[3]:

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Great resources in this answer, however, I was getting a 404 for what turned out to be a pretty silly reason:

1. I created a WiX installer for my API project
2. Installed it on a test VM (virtual machine)
3. Requested for the a URI that the API should serve
4. BANG! 404 :(

It turned out that I had missed packaging and deploying the **Global.asax** to the root of the virtual directory in my deployment. Adding this here for the benefit of goofies like myself :)

I had the same issue in a remote server, but when I execute on a localhost works fine.

My solution was:

<system.webServer>
<modules>
<remove name="UrlRoutingModule-4.0" />
<add name="UrlRoutingModule-4.0"
type="System.Web.Routing.UrlRoutingModule" preCondition="" />
</modules>
</system.webServer>

I hope, that this works for you.