Unable to launch IIS Express Web server


Everytime I try to debug my asp.net website I get this error:

Unable to launch the IIS Express Web server.

Failed to register URL "http://localhost:50010/" for site "SociopackWebAPI" application "/". Error description: The process cannot access the file because it is being used by another process. (0x80070020)

In eventviewer I noticed this error in the log:

The worker process for app pool 'Clr4IntegratedAppPool', PID='13248', failed to initialize the http.sys communication when asked to start processing http requests and therefore will be considered ill by W3SVC and terminated. The data field contains the error number.

I assume this means my Clr4IntegratedAppPool does not have enough rights? How can I fix thi?

asked on Stack Overflow Aug 3, 2017 by user2657943

3 Answers


I had exactly the same problem with VS2017 / IIS Express 10. Tried a few tips & tricks found at forums, but the only one that really fixed the bug definitively is the following:

  1. Close all Visual Studio instances and IIS Express (if it's running)
  2. Go to Windows' "Programs and Resources", find IIS Express in the list of installed programs, and "Uninstall" it
  3. Restart your computer, just be sure that all processes are closed
  4. Download IIS Express 10 standalone installer from Microsoft: https://www.microsoft.com/en-us/download/details.aspx?id=48264
  5. Install it, open Visual Studio, and it should work fine.
answered on Stack Overflow Aug 12, 2017 by Fabio Fernandes • edited May 2, 2018 by Stephen Kennedy

"The process cannot access the file because it is being used by another process" usually means that there is something else already listening on that port. Maybe you started the same application twice?

answered on Stack Overflow May 2, 2018 by Erik A. Brandstadmoen • edited May 2, 2018 by Stephen Kennedy

If you cannot find your solution for this, try this, it work for me. Window + R -> type Regedit and go to Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\HTTP chang the value of name "Start" from 4 to 3. Done.

Change this value from 4 to 3

answered on Stack Overflow Apr 7, 2019 by An LĂȘ

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