Primary NTP Server

I have been having a lot of problems configuring an OES-LINUX server as the
primary NTP server in our tree. Thru yast I set the server to get its time
from an external source, but when I have other servers use it as a
reference I get NTP polling errors. I got it working for awhile, but then
after a couple of hours it stopped again for some reason. I am using the
SuSE firewall, but opened up port 123. Does anyone have any suggestions at
to what I might be doing wrong? Thanks in advance.

Anwar Ayub