Trevor Elliott Trevor Elliott - 29 days ago 21
ASP.NET (C#) Question

"Unable to launch the IIS Express Web server" error

I receive this error when trying to launch IIS Express from Visual Studio with a project that's configured to listen to an address other than localhost. Visual Studio freezes for about 30 seconds before giving the error "Unable to launch the IIS Express Web server".

I've tried all the solutions posted to similar questions and I think I've done everything correctly. Here are the steps that I have taken:

  1. Add the following reservation to HTTP.SYS:

    netsh http add urlacl url=http://+:36899/ user=Everyone

  2. Run Visual Studio 2012 as an administrator (technically I don't think I should even have to since I set up HTTP.SYS manually).

  3. Disable Windows Firewall.

  4. Delete my IISExpress folder in my My Documents folder to ensure the default settings.

  5. Allow Visual Studio to create the entry in applicationhost.config for my web project. Then manually edit the config file to change
    which is my local IP. Then go back into the project properties in Visual Studio and change localhost to the IP and save the project so that my project is now set to

I also tried changing the port and repeating the above steps just incase the port was in use for some reason.

I want to make my IIS Express developer instance accessible from my IP on the Internet for remote testing.


The one thing that fixed this for me was using the following line in the <bindings> section for my site in the applicationhost.config file:

    <binding protocol="http" bindingInformation="*:8099:" />

The key was to simply remove localhost. Don't replace it with an asterisk, don't replace it with an IP or a computer name. Just leave it blank after the colon.

After doing this, I don't need to run Visual Studio as administrator, and I can freely change the Project Url in the project properties to the local IP or computer name. I then set up port forwarding and it was accessible to the Internet.


I've discovered one more quirk that is important to getting IIS Express to properly serve external requests.

  1. If you are running Visual Studio/IIS Express as an administrator, you must not add a reservation to HTTP.SYS using the "netsh http add urlacl ..." command. Doing so will cause an HTTP 503 Service Unavailable error. Delete any reservations you've made in the URLACL to fix this.

  2. If you are not running Visual Studio/IIS Express as an administrator, you must add a reservation to the URLACL.