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

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

Wouter3D 1

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:

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

Bruce Zhang-MSFT 3,751 Reputation points

2021-10-05T03:28:54.653+00:00

Hi @Wouter3D ,

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.
Wouter3D 1 Reputation point

2021-10-05T04:39:14.693+00:00

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.
Bruce Zhang-MSFT 3,751 Reputation points

2021-10-05T05:40:54.713+00:00

Hi @Wouter3D ,

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.
Wouter3D 1 Reputation point

2021-10-05T06:19:01.427+00:00

Correction, after setting 32bit to false I do receive an error 500.

Here are the images you asked for and a few more (web.config from wwwroot, no web.config in scripts):
Wouter3D 1 Reputation point

2021-10-05T08:54:56.687+00:00

It seems as if the problem is specific to the 32bit dll (or any other 32bit dll I tested).

I compiled a blank 64bit isapi dll and placed it in the same folder as the 32bit dll. Changed the Enable 32bit applications to false, and the 64bit dll works fine. When enable 32bit is true, the 64bit gives an error 500 as expected.
Bruce Zhang-MSFT 3,751 Reputation points

2021-10-06T07:34:24.597+00:00

Hi @Wouter3D ,

I checked this dll file and it seems a script to run VB application. Server2019 has many dll file but not include this one.

I have reproduced your issue successfully but I want to know that what the correct result is when the browser visits it. And what's the work result when it work on IIS7?
Wouter3D 1 Reputation point

2021-10-06T07:41:59.407+00:00

The AppWiz.dll file is a legacy dll file developed by my company, so it isn't a native Windows dll. It was developed in C++Builder 6. The file uses a SQL database to produce HTML pages based on the data and structure set up within the database, basically like what ASP.net would do, but completely custom logic.

When called in IIS7 the file returns either an error message in plain text, or an HTML page (generally a login page if you first connect to it).
Bruce Zhang-MSFT 3,751 Reputation points

2021-10-06T08:29:25.933+00:00

Hi @Wouter3D ,

Does this file involve your personal security information or your company's security information? Can you make a similar sample file (do not include any privacy information involving security content) and share it with me, I can use it to test. If you don't want share file, another method is you can create a support ticket from here. You will get remote support from Microsoft engineers without share files.
Wouter3D 1 Reputation point

2021-10-06T08:39:41.16+00:00

The file itself doesn't contain any security or privacy information, it simply connects with a local ini file and the database and interprets the instructions from the database.

I will send the AppWiz.dll as well as supporting dll files to you without the ini file. Running this on IIS7 gives a plain text answer that the ini file couldn't be found.

How do I send the file to you? Attachment doesn't allow dll or zip files.
Bruce Zhang-MSFT 3,751 Reputation points

2021-10-07T03:34:07.497+00:00

Hi @Wouter3D ,

Unfortunately, Q&A does not support uploading dll files. I will report this issue.

And the policy does not allow the use of third-party tools to obtain your files. Please go to the support ticket, Microsoft remote engineers will provide you with a tool to upload the dll file and solve your problem.
Wouter3D 1 Reputation point

2021-10-07T06:03:22.063+00:00

Thank you for all your assistance. Unfortunately I am unable to log a ticket using the Small Business support channel (seems to be the only way to log a Windows 2019 ticket) because I do not have a support subscription with Microsoft. Is there another way to log a ticket and receive the support I need?
Bruce Zhang-MSFT 3,751 Reputation points

2021-10-07T09:15:05.79+00:00

Hi @Wouter3D ,

No, the only way is you need to have a subscription with Micorosoft.

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

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