IIS 8.5 serving dll for download instead of execut

Question

The Problem:

When I access a (32-bit) DLL via URL like http://localhost/somepath/some.dll?action IIS always thinks I want to download the file (with file size 0 byte) instead of executing the dll.

What I tried so far:

• added an entry for this specific DLL in ISAPI- and CGI-Restrictions
• enabled the "ISAPI-dll" Handler for *.dll with feature permissions read,script and execute.
• IIS User / AppPool Identity have full access rights to the physcal location of the dll
• App-Pool is running in classic mode and 32 bit applications are enabled
• I deleted the MIME-Type Entry for *.dll

Still any browser prompts a download window. I'm running out of ideas now. I'm currently using IIS 8.5 on Windows Server 2012 R2.

The same application is running without troubles in IIS 5 on Windows 2000 SP4.

Any help or idea is appreciated!

Answer 1

And as Windows 2000 was 32-bit and Windows Server 2012 R2 is 64-bit ( and as you said your DLL is 32-bit) I expect that your issue is maybe possibly linked to this issue.

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Does your DLL has been registered on server side by using command regsvr32 <youdll> (run that command from the windows directory) ?

• You may also try to set the MIME type Entry like this:

Extension > Type

.dll > Assembly (Remove the stars and keep the dot on the extension)

• You may try to run the IIS host process in 32 bit mode

• You may try to create a wrapper of your dll's and host this wrapper dll's in COM+

Finally, according to this similar issue, you may refer to this and double check that the Handler is properly setup.

Answer 2

I know this is an old question, but what I discovered was that the web browser was actually caching the the file download. I proved this by completely stopping IIS and accessing the URL and still it prompted me to download the file. I then restarted IIS, confirmed the same issue existed still, tried from a new private window and the DLL ran instead of prompting me to download.

In short, try private mode or a different web browser after you've configured everything.