is this a physical or virtual server? take a look in the server logs and see what is goin on.
Also take a look at the enforce server and make sure nothing is going on on there like other services quitting. I have seen it only once before in a vmware enviroment... just suggestions i would have to see more. also opend a cae with symc support i wuld be interested in the outcome you can send them the logs from the servers.