Web server cannot be accessed from certain locations

I hold a web server with many domains. It is located in Israel and is behind
my ISP's firewall. a couple of days ago I started getting complaints from
people over seas that they cannot access our server. I checked DNS server
listings and all seems to be fine. There are even people that can get a
nslookup result from their DNS server (looking up my server) but cannot
access the sites via HTTP. They get a "connecting" but after a long while no
connection is made (or no data is transferred) I have not received any
complaints from people in Israel.
The server IP is: 212.179.27.198 and a sample site would be: www.ricor.com

Any ideas? How can I get down to the bottom of this?
Thanks

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Eric Yellin
Migvan Effect
Internet Solutions for Organizations
http://www.migvan.co.il
Tel: 972-8-6624444
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