Faield to start deployed web application

Question

hello community,

I am a beginner in WEB application development. During my first trial, I met with an issue when start the deployed web application onto IIS running on Windows 11. The situation is, I get below error when open the application in the Chrome.

HTTP Error 404.3 - Not Found The page you are requesting cannot be served because of the extension configuration. If the page is a script, add a handler. If the file should be downloaded, add a MIME map.

No issue observed when I start the application within Visual Studio 2022, the app is started, and the required page is opened.

Below is the steps how I did:

• Create an ASP.NET Web application project in Visual Studio 2022

• Modify the default web.config file by adding the default page to start with

• Start the app within Visual Studio

• Create a new WEB Site for the app in IIS

• Create publis profile in Visual Studio

• Publish the app onto IIS from Visual Studio

• Start Chrome, and open the application binded to localhost:85, and got the error

Here is the web.config I use, which is more or less is what was generated when create the project.

<?xml version="1.0" encoding="utf-8"?> <!-- For more information on how to configure your ASP.NET application, please visit https://go.microsoft.com/fwlink/?LinkId=169433 --> <configuration> <system.web> <compilation debug="true" targetFramework="4.8" /> <httpRuntime targetFramework="4.8" /> <pages> <namespaces> <add namespace="System.Web.Optimization" /> </namespaces> <controls> <add assembly="Microsoft.AspNet.Web.Optimization.WebForms" namespace="Microsoft.AspNet.Web.Optimization.WebForms" tagPrefix="webopt" /> </controls> </pages> </system.web> <runtime> <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1"> <dependentAssembly> <assemblyIdentity name="Antlr3.Runtime" publicKeyToken="eb42632606e9261f" /> <bindingRedirect oldVersion="0.0.0.0-3.5.0.2" newVersion="3.5.0.2" /> </dependentAssembly> <dependentAssembly> <assemblyIdentity name="Microsoft.Web.Infrastructure" publicKeyToken="31bf3856ad364e35" /> <bindingRedirect oldVersion="0.0.0.0-2.0.0.0" newVersion="2.0.0.0" /> </dependentAssembly> <dependentAssembly> <assemblyIdentity name="Newtonsoft.Json" publicKeyToken="30ad4fe6b2a6aeed" /> <bindingRedirect oldVersion="0.0.0.0-13.0.0.0" newVersion="13.0.0.0" /> </dependentAssembly> <dependentAssembly> <assemblyIdentity name="WebGrease" publicKeyToken="31bf3856ad364e35" /> <bindingRedirect oldVersion="0.0.0.0-1.6.5135.21930" newVersion="1.6.5135.21930" /> </dependentAssembly> </assemblyBinding> </runtime> <system.codedom> <compilers> <compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:default /nowarn:1659;1699;1701" /> <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:default /nowarn:41008 /define:_MYTYPE=&quot;Web&quot; /optionInfer+" /> </compilers> </system.codedom> <system.webServer> <defaultDocument> <files> <clear /> <add value="Default.aspx"/> </files> </defaultDocument> </system.webServer> </configuration>

I am sure, I do something fundematal wrongly, but till now I do not see what would it be. Please try help me.

thanks for the help /Robi

Answer 1

You need to convert your website root to an application. Right click on website and convert to application. Also be sure the app pool is .net 4

Answer 2

Hi Robert Balogh,

I gave your example a try and I think the issue might be that IIS is missing the correct handler mappings for ASP.NET.

Here’s what you can check:

1. In IIS, go to your website via the Connections panel on the left.
2. In the Features View, double-click Handler Mappings.
3. Look for the necessary mappings—especially for .aspx files like your Default.aspx.

If you don’t see them, it’s likely that IIS is missing some components needed to run the site.

To fix this:

1. Open Control Panel → Programs.
2. Go to Turn Windows features on or off.
3. Navigate to:
   Internet Information Services →
   World Wide Web Services →
   Application Development Features,
   and make sure these are checked:
   • ASP.NET 3.5
   • ASP.NET 4.5
   • ISAPI Extensions
   • ISAPI Filters
   
4. Then open Command Prompt and run iisreset to reset your IIS.

After that, go back and check the handler mappings again. If they’re showing up now, try running your app again—it should work.