"Object reference not set to an instance of an object" When Attempting to Access the App Portal Site

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Summary

When attempting to access the App Portal site, the error listed below may be seen, particularly after performing an upgrade of App Portal.

Symptoms

When attempting to access the App Portal site, the error listed below may be seen, particularly after performing an upgrade of App Portal:

Server Error in '/ESD' Application.

Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.]
SelfService.ESD.SidToHex(SecurityIdentifier sid) +9
SelfService.ESD.StartSession(Boolean bDoRedirect, String ImpersonatedAccount, String ImpersonatedComputer) +2869
ASP.default_aspx.Page_Load(Object sender, EventArgs e) +128
System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +14
System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +35
System.Web.UI.Control.OnLoad(EventArgs e) +91
System.Web.UI.Control.LoadRecursive() +74
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2207

Cause

This error will generally be thrown when the IIS authentication settings for the ESD site are set incorrectly. This will commonly occur after performing an upgrade of App Portal.

Resolution

To resolve the issue, ensure that only Windows Authentication is enabled for the ESD site in IIS. If both Anonymous and Windows Authentication are enabled, then the issue will occur. The following screen capture illustrates the appropriate authentication settings in IIS for the ESD site: