Visual Studio - IIS Express - Site won't run / connect / SSL error

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If you’ve just run Windows Update and suddenly your Visual Studio solution builds and runs but you get a browser error using IIS Express… go to your Windows Updates and look right at the bottom for the uninstall and uninstall kb5066835

Sorry for the non-Umbraco related post but hopefully this will save a few people’s sanity. Just wasted two hours of my life..

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I think this belongs here, VS with IIS Express should be a happy path for Umbraco development and this update is a showstopper for that.

You can reply to your own posts and mark as answered - might be worth doing here.

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It was a very unhappy path this afternoon! Will do Jason, thanks.

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Ran into this same issue after installing Windows Update KB5066835 but was unable to uninstall that LCU as more recent updates apparently have dependencies on this one. After much searching I found a temporary solution that involves a registry edit:

Temporary fix without uninstalling KB5066835:

  1. In the registry, navigate to:
    HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\HTTP\Parameters

  2. Under the Parameters folder, right-click in the right-hand pane and select New > DWORD (32-bit) Value.

  3. Name the value EnableHttp2Tls and set its data to 0 (zero).

  4. Repeat the process to add another DWORD (32-bit) Value named EnableHttp2Cleartext and set its data to 0.

  5. Restart the machine.

I don’t know if this will “stick” but it does allow VS + IIS + Browser to successfully run and launch the browser.

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Andy found this link, seems like it’s not just Umbraco:

For what it’s worth, your launchSettings.json has a Umbraco.Web.UI profile in it, which runs Kestrel instead and it works great. I believe it will not work if you have very IIS-specific needs, like web.config redirects (but those won’t work on Linux either then, if you ever decide to host there).

Anyway, it’s just an alternative until this is fixed, without having to uninstall or do a regedit.

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2025-10 Cumulative Update for Windows 11 Version 24H2 for x64-based Systems (KB5066835) (26100.6899) has just installed and this one worked. I guess that 26100.6899 suffix is a revised version with a fix.

Fair dos MS :slight_smile:

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Nice quick turnaround there!

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I had no idea they could / would act that fast.

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I think if you kill IIS, you do have a few million people who are going to be extremely unhappy with you, very quickly.. :sweat_smile:

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