Exchange 2016: Server error in application, OWA and ECP cannot be called up

Here I had before wrote about this problem: OWA and ECP deliver: server error in the application. The problem that OWA and ECP are no longer accessible after an update seems to occur more frequently. At least I receive mails on this topic from time to time after the release of CUs. A reader has now kindly sent me a few screenshots and an error message, here too OWA and ECP could no longer be accessed after an update of the Exchange 2016 server. In this case, the update was from CU15 to CU16. I had this problem, albeit with a different error message, but also with other Exchange versions.

Here is the text of the error message that appears when calling OWA and ECP:

Method not found: "Void Microsoft.Exchange.Security.Authentication.Utility.DeleteFbaAuthCookies(System.Web.HttpRequest, System.Web.HttpResponse)".

Description: Unhandled exception when executing the current web request. Check the stack monitor to see more information about this error and where the error was caused in the code.
Exception details: System.MissingMethodException: Method not found: "Void Microsoft.Exchange.Security.Authentication.Utility.DeleteFbaAuthCookies(System.Web.HttpRequest, System.Web.HttpResponse)".

The website then looks something like this in the browser:

The cause of the error is again one or both of the following files:

• C:\Program Files\Microsoft\Exchange Server\V15\FrontEnd\HttpProxy\SharedWebConfig.config
• C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\SharedWebConfig.config

The files do not always seem to be updated accordingly after the update. The event log also contains the event 1310 or 1309 (source ASP.NET). Both events indicate problems with the files mentioned.

So if you have a similar problem, you can easily recreate the two files. The following commands can be used to recreate the two files:

The commands can simply be executed via CMD or PowerShell. The IIS must be restarted, so the client briefly loses the connection to the Exchange Server.

Perhaps this will save some of you a longer troubleshooting process. This problem affects Exchange 2013, 2016 and most likely also Exchange 2019 servers. Even though I have not had this problem on Exchange 2019 servers so far.