KB-1178 How to disable custom error pages on IIS

A common error observed when performing activities on the Appian UI is the following:

An error was encountered while processing your request. Please try again.


An internal error has occurred.

The page could not be loaded. [HTTP Code = 500] (APNX-1-4279-001)

Native browser pop-ups with such generic errors are a result of Appian being unable to interpret the information it receives from the web server as a valid JSON object that it expects. A particular scenario where this error is encountered is described in KB-1112 where a SiteMinder configuration was causing custom HTML pages to be sent to Appian instead of JSON strings.In some cases this error may also be a result of the web server (IIS for example) hiding the actual error that Appian throws due to the fact that it has been configured to display a custom error page instead. When IIS sends this custom error page, Appian is again unable to interpret this as a valid JSON and this results in the web browser displaying the generic error text described above.

Appian errors are typically displayed within a pink box popup that provide basic information as to the root cause which IIS may be unable to determine. As such it is recommended to disable this configuration.

There are two sets of steps, both required, to disable the custom error pages on IIS to avoid they interfere with Appian http error code interpretation:

  1. Navigate to the site on IIS
  2. Select Error Pages and then Edit Feature Settings.
  3. Make sure only "Detailed Errors" is enabled.
  4. Back in the site in IIS, select .NET Error Pages and then Edit Feature Settings.
  5. Set the value to Off

If this does not resolve the issue(s) by itself, then there would at least a more meaningful error message. This along with the relevant log files should be helpful in determining the root cause of the issue(s).

Affected Versions

This article applies to all versions of Appian.

Last Reviewed: March 2017