c# there The CodeDom provider type “Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider” could not be located

there is no codedom provider defined for the language (23)

Then the problem came back. I uninstalled both Microsoft.CodeDom.Providers.DotNetCompilerPlatform and Uninstall-package Microsoft.Net.Compilers but no help. Then installed no help. Cleaned project and built no help. Restarted server no help.Then I noticed the project needed not the latest one which is currently 1.0.5 but 1.0.3 as that was the error could not load the 1.0.3 version. So I installed that dll version instead and now it works.

It's a WebApi project using VS2015.

Step to reproduce:

  1. Create an empty WebApi project
  2. Change Build output path from "bin\" to "bin\Debug\"
  3. Run

Everything is working perfectly until I changed Build Output path from "bin\" to "bin\Debug\" In fact, any Output path other than "bin\" won't work.

One little additional thing is that, having another output path to anywhere would work as long as I left a build in "bin\".

Please help providing solution to solve this. I guess that'll cost problem on actual deployment.

It stopped after publishing on the production server. The reason why it showed me this error was because it was deployed to a sub folder. In IIS i clicked right on the subfolder and excuted "Convert to application" and after this it worked.

You should update the "Microsoft.CodeDom.Providers.DotNetCompilerPlatform" and "Microsoft.Net.Compilers" packages in your project .

just uninstall the package from package manager console from command below

PM> Uninstall-package Microsoft.CodeDom.Providers.DotNetCompilerPlatform

PM> Uninstall-package Microsoft.Net.Compilers

and then install it again from nuget manager

According to your repro steps, I assumed that changing the output path in the application's property was your only change after you created the application. The only thing this change does is that it tells Visual Studio to put the output assemblies of MSBuild into the new folder. At runtime, however, ASP.Net wouldn't have any idea that it should load assemblies from this new folder instead of the \bin folder.

This answer shows the way to change the build output directory of a WebApi application. To get the exact same error showed in that post, you need to comment out the entire <system.codedom> section in web.config. And then you can follow the instructions to change the output path.

After you get your applicaiton work, you may then uncomment the <system.codedom> section. If you don't use C# 6 new syntax in your application at all you can uninstall the Microsoft.CodeDom.Providers.DotNetCompilerPlatform from you application; otherwise, you may want to add the following command line in your post-build event,

xcopy /Q /Y "$(TargetDir)roslyn\*.*" "$(TargetDir)..\roslyn\"

The new CodeDom provider always looks for the "\roslyn" folder in \bin. The above command works as a workaround and copies the \roslyn folder from your new output folder to \bin.

In my experiments, the publish tool of Visual Studio, however, published the output assemblies to the \bin folder in the deployment location regardless my output path setting. I guess your application should still work on actual deployment.

Add a reference to the CppCodeProvider assembly.

If your project has Roslyn references and you are deploying it on an IIS server , you might get unwanted errors on the website as many hosting providers still have not upgraded their servers and hence do not support Roslyn.

To resolve this issue, you will need to remove the Roslyn compiler from the project template . Removing Roslyn shouldn't affect your code's functionality. It worked fine for me and some other projects (C# 4.5.2) on which I worked.

Do the following steps:

  1. Remove from following Nuget Packages using command line shown below ( or you can use GUI of Nuget Package manager by Right Clicking on Root Project Solution and removing them ).

    PM> Uninstall-package Microsoft.CodeDom.Providers.DotNetCompilerPlatform
    PM> Uninstall-package Microsoft.Net.Compilers
  2. Remove the following code from your Web.Config file and restart IIS . ( Use this method only if step 1 doesn't solve your problem. )

      <compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:6 /nowarn:1659;1699;1701" />
      <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:14 /nowarn:41008 /define:_MYTYPE=\&quot;Web\&quot; /optionInfer+" />

Be careful of following this answer's advice. While it solves the problem at hand, it might cause different problems at a later date.

I got the same problem. Apparently the .NET compiler was not loaded to the GAC . What I did to solve it was:

First, in the package manager console type:

PM> Install-Package Microsoft.CodeDom.Providers.DotNetCompilerPlatform

Now, for some reason the nice gentlemen in Microsoft have decided not to install it to the GAC for us. You can do it manually by opening the Developer Command Prompt and typing:

gacutil -i "C:\*PATH TO YOUR APP CODE*\bin\Microsoft.CodeDom.Providers.DotNetCompilerPlatform.dll"


Microsoft try to encourage everyone to do everything with nugets which could be fine without the occasional bugs you run into with the nuget system. Try to use the same project on different solutions, accidentally (or not) update one of the many nugets it uses on one of them, and if you are unlucky you'll see what I mean when you try to build the other solution. On the other hand, putting files in the GAC can also cause future problems since people tend to forget what they put there and then when setting up new environments they forget to include these files. Another possible solution is to put the files in a central folder for 3rd party dlls (even though it's strange to call the compiler 3rd party), which creates problems of broken references when setting up new environments. If you decide to install the dll to the GAC, use caution and remember that you did so. If you don't, download the nuget for each project again and bear all the annoying bugs being caused by it (at least used to happen when I finally got sick of it and just placed the files in the GAC). Both approaches might give you headaches and create problems, it's just a question of which problems you prefer to deal with. Microsoft recommends to use the nuget system, and generally, it's better to listen to them than to an unknown programmer in SO, unless you are completely sick of the nuget system and used to deal with the GAC long enough for it to be a better alternative for you.

Ensure Internet Information Services(IIS) is enabled in Windows features on your machine.

Another possible solution could be:

Restart your Visual Studio Instance with Administrator Rights !

Here's how I resolved it:

  1. Deleted the bin folder in the project directory.
  2. Click on Build Solution . In VS2017(Run as Admin) > Build > Build Solution .

Here are my findings. I also faced this problem today's morning. I just added my current user to application pool on which application was running.


  1. Open IIS

  2. Click on application pool

  3. Select your application pool on which you are getting problem

  4. Right Click -> advanced settings

  5. Click on three dot icon beside the identiy

  6. Now select custom account

  7. Give your PC user name and Password

  8. Save

Refresh your application.. and it will start working. There was some security issue for accessing dll.

Regarding this error I've tried:

  • Cleaning and rebuilding the project
  • Unloading and reloading the project
  • Modifying the Target Framework
  • Modifying the Output path
  • Adding nuggets to the GAC
  • Deleting the packages uninstall-package Microsoft.CodeDom.Providers.DotNetCompilerPlatform uninstall-package Microsoft.Net.Compilers and installing them again.

While these all seem to be valid solutions, I was only able to generate new errors and in the end, the error seems able to display when certain references/nugets are missing.

In my case, I had recently reinstalled Microsoft Office and was referencing assemblies like Microsoft.Office.Core. The new install didn't seem to include the required packages, which made it so my solution couldn't build correctly.

I was able to solve this issue by reworking my code to the point where I didn't need to reference Microsoft.Office, but could've solved it by looking up the required packages and installing them accordingly.

Seems like an unclear error message from Visual Studio.

Just add the next nuget package to your project - Microsoft.CodeDom.Providers.DotNetCompilerPlatform .

Had the same problem.

I know it's an old thread, but I'd like to point the possible version issue of DotNetCompilerPlatform.dll, f. ex. after an update. Please check, if the new generated Web.config file is different as your released web.config, in particular the system.codedom part. In my case it was the version change from 1.0.7 to 1.0.8. The new dll had been already copied to the server, but I didn't change the old web.config (with some server special settings):

      <compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:default /nowarn:1659;1699;1701" />
      <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:default /nowarn:41008 /define:_MYTYPE=\&quot;Web\&quot; /optionInfer+" />

After I update the two lines, the error disappeared.

Go to inetmgr from start command In IIS manager console choose the application folder under Default Web Site right click on that folder then Convert to Application Run the .asmx file by Enabling It solved the problem

In my case, this happened when i change the permission of application folder and account IIS_IUSRS has been removed. After i re-added IIS_IUSRS (IIS Manager-> YourWebApp -> Edit Permission -> Add IIS_IUSRS) to the application folder and its worked.

In my case, I got the error when I had my Web Application in 4.5.2 and the referenced class libaries in 4.6.1. When I updated the Web Application to 4.5.2 version the error went away.

I was getting this error because my application pool user was set to ApplicationPoolIdentity. I changed it to a user/service account that has access to the folder and the error went away.

I just had the same problem and it was because I moved the project location and simply needed to recreate the virtual directory.

Make sure your project has fully built!

Click on 'Output' tab and make sure you don't have something like:

========== Rebuild All: 14 succeeded, 1 failed, 0 skipped =========

And open your bin folder and check to see if it's up to date.

I had a whole bunch of typescript errors that I ignored at first, forgetting that they were breaking the build and leading to there being no DLLs copied in.

Check whether the BIN folder is uploaded completely or missing in the files.

I had a number of projects in the solution and the web project (problem giving this error) was not set as the StartUp project. I set this web project as the StartUp project, and clicked on the menu item "Debug"->"Start Debugging" and it worked. I stopped debugging and then tried it again and now it’s back working. Weird.