It's also possible that the clocks really ARE skewed - assuming the threshhold Reid mentioned in the default, and it's a reasonable value (I've never had to change it and never gotten a skew error), then maybe the NTP settings on the controllers are not correct, or there is a problem with the NTP server, or there are intermittent connectivity errors. I'm not sure how DFM does it, but if it compares the controller time with the DFM server time, then perhaps the NTP issues are on the DFM server.
You can try enabling the timed.log (options time.log on) to see if it tells you anything. If DFM is a unix host, you can use ntpq to check the status of the time servers (ntpq -c lpeers - check for an asterisk by a host that tells you it's bound).
Bill