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It is not uncommon for users to encounter a 500 – Server Error while browsing applications hosted on IIS. This usually indicates a problem on the server side. But what exactly is it? To start, IIS logs an entry with a substatus code in a log file. This code is important in diagnosing what is wrong. You may also find relevant information in the system or application event log. But what if the event is not logged there? Then things get tricky and the problem becomes more difficult to solve. In such cases, understand how to work and httperror In IIS this might help.

customErrors and httpErrors: What is the difference?

Before moving on to the solutions, let us understand the differences: alignment error and httperrorThey are often confused.

To put it simply:

• alignment error Handles exceptions raised by .NET code, such as 404, 403, or 500 errors.
• httperror Handles errors generated by IIS itself, not errors generated by the application.

customErrors is part of the System.Web section that controls how .NET errors are managed. Here is a sample customError in web.config:

on the other side, httperror belong to system.webserverIt’s part of the IIS configuration. Here is an example httpErrors from IIS configuration:

Is this an IIS or .NET error? How do I say it?

The first step when troubleshooting a 500 error is to determine whether the error is occurring in the IIS pipeline or a .NET application. Activate it to isolate it. Failed Request Trace (FREB) log About the website in question. These logs provide detailed information about the request’s movement through the IIS pipeline and show which module is responsible for the error.

How to enable and read FREB logs: Reading the FREB logs can give you valuable insight into where the problem lies. You can find step-by-step guides on how to enable and analyze these logs on the Microsoft Community Hub.

Reading FREB logs, tracing failed requests: IIS request processing pipeline execution – Microsoft …

If you are experiencing 500 errors in your .NET pipeline, you may need to adjust your customErrors settings. One common approach is to temporarily disable customErrors to get more detailed error messages. This is especially useful when debugging issues in a development or staging environment.

Here’s how to set customErrors mode:

• to: The custom error page is activated. If defaultRedirect is not present, the user will see a generic error page.
• turn off: Disables custom error pages. Detailed ASP.NET errors are displayed to both local and remote clients.
• remote only: A custom error page is displayed on the remote client and detailed errors are displayed on the local server. This is the default setting.

for example:

Adjusting httpErrors in IIS module

If the error occurs in an IIS module (i.e. not related to a .NET application), consider adjusting the httpErrors setting. One useful method is to configure IIS to pass through existing responses rather than suppress them. This allows you to view the entire error and provides more context for debugging.

Here’s how to enable pass-through configuration: httperror:

This setting prevents IIS from masking the actual error response, making it easier to pinpoint the root cause.

This may not be exactly your case. Want to know more about httpErrors? Find out more here. HTTP error | microsoft run