Glad to see I'm not the only one with a problem like this.
I've got SME 6 running here at work for the last 8 months and works great until about 2 weeks ago.
We setup a SME 6 box for a client and it's working great for them reverse dns setup, email server, file server, they love it.
I setup remote access so I can monitor it for them and had been able to access it for about 3 weeks without a problem.
Suddenly I come in one Monday morning and its gone, initially I thought they'd done something silly like shut it down over the weekend. By about 10 that morning when I hadn't heard anything I thought that was it, but I still couldn't access it, no ping, no webmail, no nothing.
I can access it from home without a problem and after some stuffing around found that if I bypass the SME box and connect straight to the net I can access it from hare as well, nothing on the box had changed that weekend except for maybe a clamav update.
I still haven't got to the bottom of it (mainly because of lack of time)......