Updated: 11 October 2026 · Applies to: IIS 10 on Windows Server
This IIS error appears on Windows hosting when an ASP.NET application has settings meant for the older "Classic" pipeline but runs in "Integrated" mode.
Fix
Add this inside <configuration> in the site's web.config:
<system.webServer> <validation validateIntegratedModeConfiguration="false" /> </system.webServer>
Tip: The better long-term fix is to move handlers and modules from <system.web> to <system.webServer> so the application is designed for Integrated mode.
