Endpoint protection manager fails after installation

[AndreasM]

Hello,
we have a test environment and a productive environment.
In the test environment we could install and configure an end point protection manager.

In the production environment we get errors as these:
Cannot find path for destination inbox Notification Manager on server REGISTRY. The current component is possibly not installed.
Cannot connect to the inbox source, sleep 30 seconds and try again.  
[Software Inventory Processor (Site Trusted)] cannot update environment so skiping outbox processing.
Cannot find path for destination inbox Distribution Manager (incoming) on server registry.
~~ same goes for: Software Metering Processor Usage (Site), Success Policy Requests / Discovery Data Manager, etc.
[Notification Manager] cannot update environment so skiping outbox processing.
[Distribution Manager (Incoming)] halting execution.  
Remote site is in pull-mode.
Coult not read registy key HKEY_LOCAL_MACHINE\Software\Microsoft\SMS\MPFDM\INboxes\ on the server. The operating system reported error 2: cannot find the file

We have no clue how to resolve this. We opened a case with MS, but so far nothing.
It seems during the installation stuff from the new epp-server should be pushed onto the siteserver (and stuff should also be written in the registry of the site server,) but this fails.

The SiteServer is admin on the new Site System (we tried to install using the site servers computer account as well as the install service account - both failed).
The service RemoteRegistry runs on both systems.

Thank you for ideas.
Sincerely
Andreas

Edited May 31, 2022 by AndreasM
more tags so it can be found

[AndreasM]

When a server here is productive it gets hardened.
When things need to be installed, it can be shifted into maintenance mode.
There are changes to kerberos rights when switching modes.
This seemed to have been the problem here.