U4-8995 - Health Check in 7.5.3 showing incorrect diagnosis for Try Skip IIS Custom Errors

Created by Dan Booth 20 Sep 2016, 08:02:11 Updated by Sebastiaan Janssen 27 Oct 2016, 19:31:19

What did you do?

I upgraded a site from 7.3.8 to 7.5.3. The site is running on IIS 7.5 on Windows Server 2008r2. I then ran the Health Check > Configuration dashboard. The health check for Try Skip IIS Custom Errors said the following:

"Starting with IIS 7.5, this must be set to true for Umbraco 404 pages to show. Otherwise, IIS will takeover and render its built-in error page."

However, the check failed and recommended:

"Try Skip IIS Custom Errors is currently 'true'. It is recommended to set this to 'false' for your IIS version (7.5)."

Clicking "Fix" set trySkipIisCustomErrors="false" in umbracoSettings.config

See https://twitter.com/DanDiplo/status/778137929009029120

What did you expect to happen?

I expected the check to pass since I believe trySkipIisCustomErrors should be true when using IIS 7.5

What actually happened?

The check failed, as above, and recommended the wrong diagnosis.

2 Attachments


Sebastiaan Janssen 20 Sep 2016, 08:20:42

Problem seems to be here: https://github.com/umbraco/Umbraco-CMS/blob/dev-v7/src/Umbraco.Web/HealthCheck/Checks/Config/TrySkipIisCustomErrorsCheck.cs#L41

Eric Schrepel 11 Oct 2016, 17:49:02

And because I'm a little confused (also seeing this in 7.5.3, screencap below), what is the actual recommendation for IIS 7.5, set the TrySkipIIS... flag to True or False? When it's false, i get a ton of 404-related messages in the log files, so I assume set it to true?

Stephan 25 Oct 2016, 12:10:05

Recommended value is true, meaning Umbraco creates error pages that we want to return to the user, ie we want to ensure IIS does not replace them with its own custom (default) error pages.

Stephan 26 Oct 2016, 12:25:36

Cause: version 7.0 is NOT >= version 7.5.0, go figure fixed, PR: https://github.com/umbraco/Umbraco-CMS/pull/1549

Stephan 26 Oct 2016, 12:25:58

test: on IIS 7.5 the check should work correctly now

Priority: Normal

Type: Bug

State: Fixed


Difficulty: Very Easy


Backwards Compatible: True

Fix Submitted:

Affected versions: 7.5.0, 7.5.1, 7.5.2, 7.5.3

Due in version: 7.5.5

Sprint: Sprint 45

Story Points: 0.5