The funny thing is that I've already heard from people having set up port forwarding on their router - and at the same time the router detected a security risk on the forwarded port (too much incoming UDP packets) and blocked traffic on this port automatically - even though it has been manually forwarded.
That was the thought behind my advice to check the security logs.

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</td><td><a href="http://crawler.trillinux.org"><img align="right" style="border:0" src="http://crawler.trillinux.org/img/netsize.png" alt="Network size"></a></td></table>