Unable to access a website via the ArcGIS Web Adaptor

Description

Attempts to access a website via the ArcGIS Web Adaptor fail, and the following error message is returned:

Error:   
ArcGIS Web Adaptor
Application Error
Object reference not set to an instance of an object

Subsequent attempts to reconfigure the website and access it via the ArcGIS Web Adaptor return the same error message.

Cause

The ArcGIS Web Adaptor application component may be corrupted. This may be due to a disruption of network connectivity, causing an abrupt restart of the system where the ArcGIS Web Adaptor is installed, or incorrect configuration of the ArcGIS Web Adaptor. The disruption of network connectivity can cause the ArcGIS Web Adaptor to unregister from the server, leading to the incorrect configuration settings.

Solution or Workaround

The following workaround describes how to resolve this issue:

1. Uninstall the ArcGIS Web Adaptor application component from the system.
2. Navigate to the folder C:\inetpub\wwwroot. Delete the ArcGIS virtual directory and the problematic ArcGIS Web Adaptor folder.
3. Reinstall ArcGIS Web Adaptor and configure the new instance during the installation of the ArcGIS Web Adaptor. For more information on installing ArcGIS Web Adaptor, refer to ArcGIS Help: Installing ArcGIS Web Adaptor (IIS).
4. Ensure all the URLs are directed to the newly created instance. For more information, refer to ArcGIS Help: Configure ArcGIS Web Adaptor after installation.