IIS express: Cannot add duplicate collection entry

问题:

In Visual studio, Solution->Web.Project->Properties->Web, I have changed my Project Url from http://localhost:51123/ to http://localhost:51123/NewProjectName and I keep getting this error:

"Cannot add duplicate collection entry of type 'add' with unique key attribute 'name' set to ...." on every module added.

Adding a remove tag works but then it should have been a problem even before i changed the url. Any suggestions?

回答1:

I think IIS Express probably has 2 <application>-blocks and both will be pointing to the same physicalPath.

Go to the IIS Express config file in: My Documents\IISExpress\config\applicationhost.config

Search for NewProjectName

Change the physicalPath for the root application to something else. Point it to an empty folder.

Should look something like this:

<site name="NewProjectName" id="1">
  <application path="/" applicationPool="Clr4IntegratedAppPool">
    <virtualDirectory path="/" physicalPath="c:\Temp" />
  </application>
  <application path="/NewProjectName" applicationPool="Clr4IntegratedAppPool">
    <virtualDirectory path="/" physicalPath="c:\sourcecode\NewProjectName" />
  </application>
  <bindings>
    <binding protocol="http" bindingInformation="*:51123:localhost" />
  </bindings>
</site>

回答2:

Also, ensure you don't have a duplicate web.config file in one of the parent folders (eg: a web.config backup file). That was the issue with mine!

回答3:

I started randomly getting this error. I noticed that the iis express had two sites.

This double layer is causing IIS to read the web.config from the first site and second at \WFM. therefore finding duplicates. I just stopped all the sites and removed the \WFM from my web project path. However you could go clear the files and folders from your temp file in IIS express. In my case I had multiple versions of the solution and one solution's project\user config had an extra path in the web project URL. VS 2015 added it, or someone checked in their own user config to TFS. Hope this helps others.

回答4:

If you create an IIS website with the physical path the same as the project folder, and then use it create a virtual folder for the project, you are going to see this issue.
Your Web.config file is being loaded twice.
Instead as orjanto pointed out, create an empty folder and point the IIS website to it and then use it to create a virtual folder from Visual Studio.

回答5:

All web.config files work off multiple cascading levels of inheritance at the machine, IIS, project, and folder level locations, with each providing a higher degree of specificity.

If you're getting this error, it means you've either:

1. Added the same key twice in the same file (unlikely since you would've seen it)
2. The same key already exists in a separate file higher up the inheritance chain

There can be a lot of different root causes for #2, but if you want to side step them, you can just remove any previous declarations and then re-add your own at that level (I'd pay good money for an upsert feature).

So just add <remove> tags like this for any offending elements:

<system.webServer>
  <modules runAllManagedModulesForAllRequests="true">

    <remove name="ErrorLog" />
    <remove name="ErrorMail" />
    <remove name="ErrorFilter" />

    <add name="ErrorLog"    type="Elmah.ErrorLogModule, Elmah"    preCondition="managedHandler" />
    <add name="ErrorMail"   type="Elmah.ErrorMailModule, Elmah"   preCondition="managedHandler" />
    <add name="ErrorFilter" type="Elmah.ErrorFilterModule, Elmah" preCondition="managedHandler" />

  </modules>
</system.webServer>

回答6:

My Project Url in Web tab inside project properties pointed to wrong url and I was not able to change it ("Would you like to create Virtual Directory?" and VS was locked in a loop (Yes -> Unable to create, No -> Operation Canceled) until I manually reverted Url to the (incorrect) state it was before. The solution was to run VS as Admin. I was able to change that url and everything started to work. Hope it helps!

回答7:

You may find that after upgrading to the latest windows 10 service pack June 2017, this issue is because certain nodes seem to now appear under the root config (machine.config). I removed my duplicates from web.config and it all worked again.

回答8:

I had a problem of same type. Running my site published on IIS, the same error was shown.

I saw a web.config file in the wwwroot folder (out of application folder). I removed this file and the application ran OK.

Look for a web.config file placed in a wrong folder (above your folder application).

Good luck!

回答9:

The answer that @orjanto posted solved the problem for me, but I had an additional problem on top of that. After fixing, Internet Explorer still thought that my HTML page was a directory instead of a file.

I had duplicates in my IIS Express config file:

<site name="MyAPI" id="56">
     <application path="/" applicationPool="Clr4IntegratedAppPool">
          <virtualDirectory path="/" physicalPath="C:\source\repos\MyAPI" />
     </application>
     <application path="/login.html" applicationPool="Clr4IntegratedAppPool">
          <virtualDirectory path="/" physicalPath="C:\source\repos\MyAPI" />
     </application>
     <bindings>
          <binding protocol="http" bindingInformation="*:57018:localhost" />
          <binding protocol="https" bindingInformation="*:44302:localhost" />
     </bindings>
 </site>

Note the path="/login.html" in the second <application> entry.

My page was redirecting to "localhost:57018/login.html/" like it was a directory.

Removing the second entry fixed the problem with the configuration file duplicates, however I continued to have a problem where Internet Explorer seemed to think that /login.html/ was a directory (Internet Explorer 11). To diagnose the problem, I checked Chrome and Chrome worked fine.

I went into Internet Explorer, went to Tools > Internet Options > General Tab. Then under "Browsing History" section, I deleted History, Cookies and Website Data, & Temp. Internet Files.

回答10:

I had the same problem. It turned out that I had a different project that uses IISExpress with the same port number. Once I changed the project to use a different port number, the error went away.

回答11:

I had the same problem, here's what I did:

• I changed my Server settings from Local IIS to IIS Express:

• If it still doesn't work, I changed the port number to different port number then click the Create Virtual Directory button. Clean the solution then Rebuild.

回答12:

Just Change the port number which is not yet used by another application and it works