WebApi s message an error has occurred on IIS7 not in IIS Express

Question

I m working with ASP NET MVC 4 WebApi and am having a lot of fun with it running it on my local computer on IIS Express   I ve configured IIS Express to serve remote machines too  and so other s in my company are using my computer as our webserver    After deciding this was a less-than-optimal solution  we decided to put the WebApi on a remote server after installing  NET 4 5   When I use fiddler and sent a POST to a controller on my local machine it returns the correct response  yet when I change the domain to the webserver running IIS7 the same POST returns a cryptic        message   an error has occurred      message   Anyone have any idea what could be going on

User · Answer

I always come to this question when I hit an error in the test environment and remember, "I've done this before, but I can do it straight in the web.config without having to modify code and re-deploy to the test environment, but it takes 2 changes... what was it again?"

For future reference

<system.web>
   <customErrors mode="Off"></customErrors>
</system.web>

AND

<system.webServer>
  <httpErrors errorMode="Detailed" existingResponse="PassThrough"></httpErrors>
</system.webServer>

User · Answer

I had a similar problem when posting to the WebAPI endpoint  By turning the CustomErrors Off  i was able to see the actual error which is one of the dlls was missing

User · Answer

So i tried all the suggested solutions to no avail  All i did was to set run the app from the server and it displayed the error in full  this should have worked when i set customErrors mode to false but it didn t  The moment i browsed the API form the server i was able to see the problem

User · Answer

If you have  lt deployment retail  true   gt  in your  NET Framework s machine config  you won t see detailed error messages  Make sure that setting is false  or not present

User · Answer

The problem was a missing dependency that wasn t on the server but was on my local machine   In our case  it was a Devart Data Linq dll   To get to that answer  I turned on IIS tracing for 500 errors   That gave a little bit of information  but the really helpful thing was in the web config setting the  lt system web gt  lt customErrors mode  Off   gt  lt  system web gt  This pointed to a missing dynamically-loaded dependency   After adding this dependency and telling it to be copied locally  the server started working

User · Answer

In case this helps anyone   I had a similar issue  and following Nates instructions I added    lt system web gt        lt customErrors mode  Off   gt    lt  system web gt    This showed me more information about the error       ExceptionMessage    Unable to load the specified metadata resource        ExceptionType    System Data Entity Core MetadataException       StackTrace       at     System Data Entity Core Metadata Edm MetadataArtifactLoaderCompositeResource LoadResources       This is when I remembered that I had moved the edmx file to a different location and had forgotten to change the connectionstrings node in the config  connectionsstrings node was placed in a seperate file using  configSource   but that s another story

User · Answer

My swagger XML file was not deployed into  bin   GlobalConfiguration Configuration    EnableSwagger c   gt          c SingleApiVersion  v1    SwaggerDemoApi        c IncludeXmlComments string Format    0  bin SwaggerDemoApi XML                             System AppDomain CurrentDomain BaseDirectory        c DescribeAllEnumsAsStrings           http   wmpratt com swagger-and-asp-net-web-api-part-1     It had to be set in the Release Configuration as well as in the Debug Configuration

User · Answer

None of the other answers worked for me   This did   in Startup cs   public class Startup       public void Configuration IAppBuilder app                var config   new HttpConfiguration             WebApiConfig Register config               Here           config IncludeErrorDetailPolicy   IncludeErrorDetailPolicy Always             or you can put it in WebApiConfig cs    public static class WebApiConfig       public static void Register HttpConfiguration config                   Web API routes         config MapHttpAttributeRoutes             config Routes MapHttpRoute              name   DefaultApi               routeTemplate   api  controller   action   id                defaults  new   id   RouteParameter Optional                          Here           config IncludeErrorDetailPolicy   IncludeErrorDetailPolicy Always

User · Answer

Basically   Use IncludeErrorDetailPolicy instead if CustomErrors doesn t solve it for you  e g  if you re ASP NET stack is  2012    GlobalConfiguration Configuration IncludeErrorDetailPolicy    IncludeErrorDetailPolicy Always    Note  Be careful returning detailed error info can reveal sensitive information to  hackers   See Simon s comment on this answer below   TL DR version  For me CustomErrors didn t really help  It was already set to Off  but I still only got a measly an error has occurred message  I guess the accepted answer is from 3 years ago which is a long time in the web word nowadays  I m using Web API 2 and ASP NET 5  MVC 5  and Microsoft has moved away from an IIS-only strategy  while CustomErrors is old skool IIS      Anyway  I had an issue on production that I didn t have locally  And then found I couldn t see the errors in Chrome s Network tab like I could on my dev machine  In the end I managed to solve it by installing Chrome on my production server and then browsing to the app there on the server itself  e g  on  localhost    Then more detailed errors appeared with stack traces and all   Only afterwards I found this article from Jimmy Bogard  Note  Jimmy is mr  AutoMapper    The funny thing is that his article is also from 2012  but in it he already explains that CustomErrors doesn t help for this anymore  but that you CAN change the  Error detail  by setting a different IncludeErrorDetailPolicy in the global WebApi configuration  e g  WebApiConfig cs    GlobalConfiguration Configuration IncludeErrorDetailPolicy    IncludeErrorDetailPolicy Always    Luckily he also explains how to set it up that webapi  2  DOES listen to your CustomErrors settings  That s a pretty sensible approach  and this allows you to go back to 2012  P   Note  The default value is  LocalOnly   which explains why I was able to solve the problem the way I described  before finding this post  But I understand that not everybody can just remote to production and startup a browser  I know I mostly couldn t until I decided to go freelance AND DevOps

[iis-7] WebApi's {"message":"an error has occurred"} on IIS7, not in IIS Express

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