"An exception occurred while processing your request. Additionally, another exception occurred while executing the custom error page..."

Question

I'm trying to publish an MVC website as an Azure webrole.

When I run it locally, everything works fine.

But once I publish it to Azure and surf to some MVC action, I get this error:

Server Error in '/' Application.

Runtime Error

Description: An exception occurred while processing your request. Additionally, another exception occurred while executing the custom error page for the first exception. The request has been terminated.

I don't understand how the error handler can encounter an exception, because errors are handled in the default way:

public class FilterConfig {     public static void RegisterGlobalFilters(GlobalFilterCollection filters)     {         filters.Add(new HandleErrorAttribute());     } } 

This is my web.config:

<?xml version="1.0"?>  <configuration>   <configSections>     <sectionGroup name="system.web.webPages.razor" type="System.Web.WebPages.Razor.Configuration.RazorWebSectionGroup, System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">       <section name="host" type="System.Web.WebPages.Razor.Configuration.HostSection, System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />       <section name="pages" type="System.Web.WebPages.Razor.Configuration.RazorPagesSection, System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />     </sectionGroup>   </configSections>    <system.web.webPages.razor>     <host factoryType="System.Web.Mvc.MvcWebRazorHostFactory, System.Web.Mvc, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />     <pages pageBaseType="System.Web.Mvc.WebViewPage">       <namespaces>         <add namespace="System.Web.Mvc" />         <add namespace="System.Web.Mvc.Ajax" />         <add namespace="System.Web.Mvc.Html" />         <add namespace="System.Web.Routing" />       </namespaces>     </pages>   </system.web.webPages.razor>    <appSettings>     <add key="webpages:Enabled" value="false" />   </appSettings>    <system.web>         <httpHandlers>       <add path="*" verb="*" type="System.Web.HttpNotFoundHandler"/>     </httpHandlers>      <pages         validateRequest="false"         pageParserFilterType="System.Web.Mvc.ViewTypeParserFilter, System.Web.Mvc, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"         pageBaseType="System.Web.Mvc.ViewPage, System.Web.Mvc, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"         userControlBaseType="System.Web.Mvc.ViewUserControl, System.Web.Mvc, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">       <controls>         <add assembly="System.Web.Mvc, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" namespace="System.Web.Mvc" tagPrefix="mvc" />       </controls>     </pages>   </system.web>    <system.webServer>     <validation validateIntegratedModeConfiguration="false" />      <handlers>       <remove name="BlockViewHandler"/>       <add name="BlockViewHandler" path="*" verb="*" preCondition="integratedMode" type="System.Web.HttpNotFoundHandler" />     </handlers>   </system.webServer> </configuration> 

This is Error.cshtml:

@model System.Web.Mvc.HandleErrorInfo  @{     ViewBag.Title = "Error"; }  <h2>     Sorry, an error occurred while processing your request. </h2> 

What can cause this exception, and why can't I reproduce it locally?

Answer 1

First, set customErrors = "Off" in the web.config and redeploy to get a more detailed error message that will help us diagnose the problem. You could also RDP into the instance and browse to the site from IIS locally to view the errors.

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

First guess though - you have some references (most likely Azure SDK references) that are not set to Copy Local = true. So, all your dependencies are not getting deployed.

Get to the detailed error first and update your question.

UPDATE: A second option now available in VS2013 is Remote Debugging a Cloud Service or Virtual Machine.

Answer 2

I wasn't using Azure, but I got the same error locally. Using <customErrors mode="Off" /> seemed to have no effect, but checking the Application logs in Event Viewer revealed a warning from ASP.NET which contained all the detail I needed to resolve the issue.