So I managed to deal with the problem on my own.
I had a error on the time due to my Location in Germany.
To solve the problem I completed the tasks on https://forum.rockstor.com/t/solved-unable-to-check-update-due-to-a-system-error-time-data-mo-20-jun-2016-does-not-match-format-a-d-b-y/2178/3