NTP - no server suitable for synchronization found

If you get this error when configuring NTP:

[root@server ~]# ntpdate -d 192.43.244.18
24 Jun 23:16:10 ntpdate[17897]: ntpdate 4.2.0a@1.1190-r Sat May 5 12:55:37 EDT 2007 (1)
Looking for host 192.43.244.18 and service ntp
host found : 192.43.244.18
transmit(192.43.244.18)
transmit(192.43.244.18)
transmit(192.43.244.18)
transmit(192.43.244.18)
transmit(192.43.244.18)
192.43.244.18: Server dropped: no data
server 192.43.244.18, port 123
stratum 0, precision 0, leap 00, trust 000
refid [192.43.244.18], delay 0.00000, dispersion 64.00000
transmitted 4, in filter 4
reference time: 00000000.00000000 Thu, Feb 7 2036 1:28:16.000
originate timestamp: 00000000.00000000 Thu, Feb 7 2036 1:28:16.000
transmit timestamp: cded788d.d27253da Wed, Jun 24 2009 23:16:13.822
filter delay: 0.00000 0.00000 0.00000 0.00000
0.00000 0.00000 0.00000 0.00000
filter offset: 0.000000 0.000000 0.000000 0.000000
0.000000 0.000000 0.000000 0.000000
delay 0.00000, dispersion 64.00000
offset 0.000000

24 Jun 23:16:14 ntpdate[17897]: no server suitable for synchronization found
[root@server ~]#

SOLUTION: A network device is blocking the communication, trace the packets and find where they are getting blocked.

[root@server ~]# ntpdate -d 192.43.244.18
24 Jun 23:31:15 ntpdate[17926]: ntpdate 4.2.0a@1.1190-r Sat May 5 12:55:37 EDT 2007 (1)
Looking for host 192.43.244.18 and service ntp
host found : 192.43.244.18
transmit(192.43.244.18)
receive(192.43.244.18)
transmit(192.43.244.18)
receive(192.43.244.18)
transmit(192.43.244.18)
receive(192.43.244.18)
transmit(192.43.244.18)
receive(192.43.244.18)
transmit(192.43.244.18)
server 192.43.244.18, port 123
stratum 1, precision -29, leap 00, trust 000
refid [ACTS], delay 0.15309, dispersion 0.00023
transmitted 4, in filter 4
reference time: cded7be0.eeccc6ad Wed, Jun 24 2009 23:30:24.932
originate timestamp: cded7c14.8761f57d Wed, Jun 24 2009 23:31:16.528
transmit timestamp: cded7c14.739e279d Wed, Jun 24 2009 23:31:16.451
filter delay: 0.15407 0.15309 0.15320 0.15765
0.00000 0.00000 0.00000 0.00000
filter offset: 0.010252 0.010024 0.010108 0.011162
0.000000 0.000000 0.000000 0.000000
delay 0.15309, dispersion 0.00023
offset 0.010024

24 Jun 23:31:16 ntpdate[17926]: adjust time server 192.43.244.18 offset 0.010024 sec