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Wouter3D-7318 asked BruceZhang-MSFT commented

IIS 10 ISAPI DLL giving 404.0 error on dll file after enabling it

I've been working with isapi.dll files on IIS for years, up to IIS 7.0.

I am now trying to migrate my Server 2008R2 to Server 2019. I have done everything I know, but nothing seems to work.

Here is what I've done:

  1. Made sure the server Roles & Features for the Web Server includes CGI, ISAPI Extensions, and ISAPI Filters. I've even removed and re-added all these features to make sure there wasn't a problem when first installing them.

  2. On IIS Manager, on the default site, I added a new application (scripts) and made sure the dll file with all supporting files are in this folder (exactly the files that work on IIS 7.0).

  3. If you open the dll file in a browser, it tries to download the file, which means my IIS server works, the application folder alias works, and IIS found the dll file.

  4. On the application folder's Handler Mapping, I enabled CGI and ISAPI.dll by ticking Execute on Edit Feature Permissions.

  5. If you open the dll on the server browser now, you receive a 404.2 error, stating that you have not added the dll to the CGI and ISAPI Restrictions List, which means it is recognizing that the dll file as an ISAPI dll file.

  6. In IIS Manager, on the server tab on the left, opening the CGI and ISAPI Restriction feature, added the dll file and made sure to Allow access. I also tried to update the Feature Settings to enable all unspecified DLL and CGI files, just to cover all bases.

  7. Now, if you open the dll in the browser you should see some results (even if it is an error 500 if some supporting files or database connections don't work), but instead I get a 404.0 error that the file is missing or moved.

I have tried every possible combination of all the suggestions on the web, but effectively all of them come back to the steps above.

Any assistance to point me in the right direction will be helpful.

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Hi @Wouter3D-7318 ,

At step4, did you enable ISAPI-dll?

I checked all your steps and all of them are correctly. Is your dll file 32-bit or 64-bit? If it is 32-bit, you also need to enable 32bit applications on application pool.

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Thank you for your comment. Yes, this is exactly what I did in step 4 by ticking the Execute permission for the feature.

I did enable 32bit. If you don't you should receive an error 500, but even with this I receive a 404.0 error.

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Hi @Wouter3D-7318 ,

I try to reproduce the issue but failed. Can you show the following images about this issue: the list of sub items under Application Development in Server Manager, the location of dll file, complete 404 error page, the binding of site and web.config.

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