Am I understanding you correctly that the clock on the Vista taskbar just
stops at a certain time? So for example it keeps good time until 3:14 and
then just stays at 3:14? If that is the case, I'd be surprised if it is
related to the SBS.
Open a cmd prompt on a machine where the time is stopped. Type "net time
\\machinename" without the quotes and where machinename is the name of the
Vista PC. Does the resulting time match the stopped time on the tray clock,
or is it the correct time? Now in the same cmd window type "net time \\sbs"
where sbs is the name of your SBS. Does the result indicate that the time
is correct on the SBS?
When this happens to multiple Vista PCs, is it always at the same time, or
is it random across all the effected machines? When a machine exhibits
this, is it otherwise responsive? Can you look in Task Manager and see if
there are free resources? I have seen 100% CPU situations where the clock
display would stop changing until the CPU usage drops - could you be seeing
something like that?
Any scheduled tasks, backup, etc. running when this happens? Anything in
the system or application logs on the Vistas or the SBS? Is there any user
action that seems to trigger it? Anything installed, changed, or updated
prior to this starting?
One comment: if the tray clock display is stopped at a particular time, but
the net time command indicates the correct time (on the local PC, not the
SBS), IMO that pretty conclusively rules out the SBS as the source. I would
be surprised if the SBS were involved regardless - time sync does not happen
that often, so even if the SBS somehow continuously reported the same time
for a long period, that would not cause the workstations' time to stop
changing. The workstation would sync to the (incorrect) time on the SBS,
but then it would continue to keep time until its next sync. Also, if the
Vista PCs' clocks actually stopped (as opposed to just displaying
incorrectly), you would lose the ability to log into the domain due to the time
discrepancy between the workstations and the server.