Occasionally you need to be able to run two instances of Visual Studio to debug two different web applications simultaneously. If these web applications are set up to run in IIS, you may get the following error when you try to attached the second debugger: Unable to start debugging on the web server. A debugger is already attached. To run your applications, IIS creates a worker processes for each “Application Pool” you define in the IIS configuration. It then runs all applications assigned to a given App Pool in the same process. Since only one VS debugger can be attached to any given process at a time, simply putting your web apps in different App Pools is
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Today I got the following error after setting a web site in IIS to use HTTPS/SSL and trying to start the site: “The process cannot access the file because it is being used by another process. (Exception from HRESULT: 0x80070020)” Not a very helpful error message. Fortunately, I remember seeing something like this before when another application was already using port 80 or 443 (the standard HTTP and HTTPS ports) and IIS couldn’t attach to them. In this case it was that ubiquitous communications tools for developers and non-developers alike: Skype. Skype has an advanced setting that allows it to use ports 80 and 443 to accept incoming connections, but this doesn’t
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