Thx GSparks for the Answer, the vmware support told us the same but it doesnt make any changes on that problem :-(.
Sorry that the answer took so long but yesterday we had a power outage and had problems with timesync.
Today I tested everything also delete the old restorepoints and created a new fresh backup after the UAC was switched off on all computers but the same result and the same error messages "Login failed. Could not find vm at <ip>" and also it is still in the https://vcenter/mob / the same that for the server with the problem I can not find ip entrys.
The UAC solved just the problem that we where able to install on the sql server the vmware vdp sql agent without error message.
But also when I try to make a backup via SQL server he says there are no registered servers, on the sql firewall is open in all direction.
We also restarted after UAC was switched off the hole server environment to be on the save side the setting was applied.
What else we can check?
best regards