Self Service E-Mail Registration failes on Certificate


Self Regsitration by User seems to be working fine, but not by creating it in UMC


Traceback (most recent call last):
  File "/usr/bin/univention-run-diagnostic-checks", line 144, in <module>
  File "/usr/bin/univention-run-diagnostic-checks", line 76, in main
    client = Client(None, args.username, args.password)
  File "/usr/lib/python2.7/dist-packages/univention/lib/", line 371, in __init__
    self.authenticate(username, password)
  File "/usr/lib/python2.7/dist-packages/univention/lib/", line 384, in authenticate
    return self.umc_auth(username, password)
  File "/usr/lib/python2.7/dist-packages/univention/lib/", line 494, in umc_auth
    return self.request('POST', 'auth', data)
  File "/usr/lib/python2.7/dist-packages/univention/lib/", line 524, in request
    return self.send(request)
  File "/usr/lib/python2.7/dist-packages/univention/lib/", line 549, in send
    raise ConnectionError('Could not send request.', reason=exc)
univention.lib.umc.ConnectionError: ('Could not send request.', CertificateError("hostname 'ucs.sysops.local' doesn't match either of '', ''",))

Any Idea where to start fixing this and bringing it to work?
I can create Users, but no Mail is being created!