ical server not responding

working with OS X 10.8.2 with server installed. For the past 6 months no problems what soever with iCal server working in a 30 computer local network. Everyone could login, make appointments, etc. Then suddenly on the Server app, this error message appears. Also the delegations have dissapeared and no clients are able to access the iCal server data, make changes or new schedules.

Would appreciate anyone help and advise in order to resolve this problem.