well better to do a correct connect than a lazy connect
you/i dont know what port he is running the server on
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have you tried changing the server port to something like 27030 and forward that? and please list down what ports you are actually forwarding
damn it. let's fix this lol!!! :S
clearly a router/portforward issue because he said "only i can join cause it use LAN ip" but when he connects with wan ip. the port says inuse which normally shows up when its actually in use or not forwarded correctly
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and i dugg up a mailing list
http://www.mail-archive.com/hlds@lis.../msg08080.html
could be the firmware as well. also try a update and also try dark masters suggestion
TRY evERyth1ng