BEA-141149 invalid attempt was made to connect to the Administration Server

Last days spent some time on an issue that a managed server on a remote server was not able to connect to the admin server. Log in the admin console showed the following error:

####<Aug 2, 2016 8:13:47 AM CEST> <Error> <Management> <sahwlsdXXYYZZ.corp.XXYYZZ.com> <AdminServer> <[ACTIVE] ExecuteThread: '0' for queue: 'weblogic.kernel.Default (self-tuning)'> <<anonymous>> <> <a31650b4-48fe-4b71-837a-80dfa6caf0d9-0000001e> <1470118427330> <[severity-value: 8] [rid: 0] [partition-id: 0] [partition-name: DOMAIN] > <BEA-141149> <An invalid attempt was made to connect to the Administration Server with a salt of n+Aj1CJZPev9gLWFjKvxQw== and a signature of o0BE/0lZi+TsHRrngSUCPrIgge6gFbfNznsdbirx1Tc=, likely due to private key mismatch.>

The domain consisted of one AdminServer and two managed servers. The first managed server was together on the same machine as the AdminServer and started fine. The second managed server on another machine failed to start. 

Long story short. On both servers there were no active ntp deamons, resulting in a time differences of 6 minutes. And the timestamp is part of the encryption. Activating the ntp daemon fixed this issue.