Time Sync errors - W32Time

Our client computers are receiving the following error:


The time provider NtpClient is configured to acquire time
from one or more time sources, however none of the sources
are currently accessible. No attempt to contact a source
will be made for 29 minutes. NtpClient has no source of
accurate time.

The time provider NtpClient was unable to find a domain
controller to use as a time source. NtpClient will try
again in 30 minutes.

Could this cause a computer to get disconnected from the
server, if so, how can we fix this problem so that this
error does not occur. We are running Small Business
Server 2003.

Any help appreciated.

Thanks!!!

Valeria