Problems with RDS webfeeds : Object not found

Hi everyone

after changing the name of our domain, I cannot access https://<fqdnServerName>/rdweb/feed/webfeed.aspx anymore. I always get following entry in windows event log. (Sorry, some german messges). This is Windows Server 2016, all current patches applied.

1. Event code:3005
2. Event message:Unhandled Exception
3. Event time:28.10.202015:11:04
4. Event time(UTC):28.10.202014:11:04
5. Event ID: c867a015176c469c911e13adb6b14329
6. Event sequence:4
7. Event occurrence:1
8. Event detail code:0
10. Application information:
11. Application domain:/LM/W3SVC/1/ROOT/RDWeb/FeedLogin-7-132483678646248403
12. Trust level:Full
13. ApplicationVirtualPath:/RDWeb/FeedLogin
14. ApplicationPath: C:\Windows\Web\RDWeb\FeedLogin\
15. Machine name: XXXX
17. Process information:
18. Process ID:9000
19. Process name: w3wp.exe
20. Account name: IIS APPPOOL\RDWebAccess
22. Exception information:
23. Exception type:NullReferenceException
24. Exception message:DerObjektverweis wurde nicht auf eineObjektinstanz festgelegt.
25. bei Microsoft.TerminalServices.Publishing.Portal.FormAuthentication.WebFeedLoginHandler.ProcessRequest(HttpContext context)
26. bei System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
27. bei System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step)
28. bei System.Web.HttpApplication.ExecuteStep(IExecutionStep step,Boolean& completedSynchronously)
32. Request information:
33. Request URL: https://<fqdn>/RDWeb/FeedLogin/WebFeedLogin.aspx
34. Request path:/RDWeb/FeedLogin/WebFeedLogin.aspx
35. User host address:::1
36. User:
37. Is authenticated:False
38. AuthenticationType:
39. Thread account name: IIS APPPOOL\RDWebAccess
41. Thread information:
42. Thread ID:55
43. Thread account name: IIS APPPOOL\RDWebAccess
44. Is impersonating:False
45. Stack trace: beiMicrosoft.TerminalServices.Publishing.Portal.FormAuthentication.WebFeedLoginHandler.ProcessRequest(HttpContext context)
46. bei System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
47. bei System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step)
48. bei System.Web.HttpApplication.ExecuteStep(IExecutionStep step,Boolean& completedSynchronously)
51. Customevent details:

I set up RDWeb on a temporary Server which works fine. I cannot find any major differences though.

Since I am far away from being an IIS expert, any help is appreciated! I cannot find any relevant logs except the event log entry.

I found some posts about uninstalling some .net 4.6.1 related kbs on Windows Server 2012. But I have a 2016 and cannot find any .net reference.

Any ideas?

Thank you!

SebNeu