ERROR: ProtocolError: <ProtocolError for satellite.rhn.redhat.com /SAT: 500 Internal Server Error>

From my satellite server's log:

2015/05/18 14:09:54 -00:00 Commandline: ['/usr/bin/satellite-sync', '-c', 'rhn-tools-rhel-x86_64-server-7']
2015/05/18 14:09:54 -00:00 Red Hat Satellite - live synchronization
2015/05/18 14:09:54 -00:00 url: https://satellite.rhn.redhat.com
2015/05/18 14:09:54 -00:00 debug/output level: 1
2015/05/18 14:09:55 -00:00 ERROR: ProtocolError:
2015/05/18 14:09:55 -00:00
2015/05/18 14:09:55 -00:00
ERROR: there was a problem synchronizing the information.
Error message:

any suggestions?