Unable To Launch Web Server

Question

I have asp.net web application project in visual studio 2012. When I want to start it, I have the following error:

Unable to launch the IIS Express Web server: P

Answer 1

Try the following steps:

1. In VS2013 Opened Debug > Website Properties.
2. Select the "Web" tab.
3. Under "Servers" I found "Override application root URL" was unchecked. I checked it and saved.

Answer 2

I had the exact same problem that the OP states "This problem came from nothing."

And I simply just rebooted my machine and it worked again. Restarting IIS Express didn't work.

Answer 3

Much more likely than any of the above answers: delete IISExpress folder, as described in this SO article.

Answer 4

Killing the IIS Express Worker Process solves this for me; I run into this while trying to debug two concurrent instances of Visual Studio 2015 and switching between the two web solutions.

If this is a constant problem then Kedar's answer of modifying the solution is better, but in a pinch, for a code review, etc I prefer this.

Answer 5

In web.csproj change the port number

<DevelopmentServerPort>56048</DevelopmentServerPort>

Answer 6

If this situation is sudden (everything works ok, but suddenly the error Unable to launch the IIS Express Web server is shown) the solution that often works for me is simply:

• Kill IISExpress process
• More importantly, close all browsers processes (Firefox, Chrome, Chrome Dev Tools, IE, etc)

Works like a charm :) If doesn't, try different solutions from this thread.

PS. I post it as an answer so it can be found easily, although someone wrote it here somewhere in a comment.