Added 500.30 Key Vault note - a common issue (#16597)

aspnetcore/test/troubleshoot-azure-iis.md

@@ -5,7 +5,7 @@ description: Learn how to diagnose problems with Azure App Service and Internet
 monikerRange: '>= aspnetcore-2.1'
 ms.author: riande
 ms.custom: mvc
-ms.date: 01/10/2020
+ms.date: 01/18/2020
 uid: test/troubleshoot-azure-iis
 ---
 # Troubleshoot ASP.NET Core on Azure App Service and IIS
@@ -111,7 +111,10 @@ The worker process fails. The app doesn't start.
 
 The [ASP.NET Core Module](xref:host-and-deploy/aspnet-core-module) attempts to start the .NET Core CLR in-process, but it fails to start. The cause of a process startup failure can usually be determined from entries in the Application Event Log and the ASP.NET Core Module stdout log.
 
-A common failure condition is the app is misconfigured due to targeting a version of the ASP.NET Core shared framework that isn't present. Check which versions of the ASP.NET Core shared framework are installed on the target machine.
+Common failure conditions:
+
+* The app is misconfigured due to targeting a version of the ASP.NET Core shared framework that isn't present. Check which versions of the ASP.NET Core shared framework are installed on the target machine.
+* Using Azure Key Vault, lack of permissions to the Key Vault. Check the access policies in the targeted Key Vault to ensure that the correct permissions are granted.
 
 ### 500.31 ANCM Failed to Find Native Dependencies