I downloaded/installed Windows updates KB4568831 and KB4562899 (both previews) today, and suddenly all my apps in IIS started producing HTML status code 500.19, which normally indicates that the application pool identity account does not have access to the application folders. None of my permissions changed, so that seemed like a red herring. As soon as I rolled the updates back, everything started working as before. I am hopeful someone else may have some suggestions on what went wrong.

Before I rolled back:

  • I rebooted my machine twice.
  • I restarted IIS.
  • I double/triple-checked all the permissions on my folders to ensure the app pool identities had access.
  • I saw some errors in the Event Viewer that suggested that the AppHostSvc was having trouble deleting inetpub history folders, so I both a) deleted the folders by hand, and b) restarted the service; neither helped.

1 Answer 1


On my machine, after installation of KB4568831, IIS-Manager shows in "Feature Delegation" at least three changes which corrupts all my web applications:

  1. Modules set on "readonly" (instead of "read/write")
  2. Handlers set on "readonly" (instead of "read/write")
  3. SessionState is missing (should be present with "read/write")

After rollback (deinstallation of KB4568831), all things are ok.

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