I have had quite a few problems with tunneling issues as I had posted before. I had a lan and a couple of friends joined from outside and all was working then suddenly is stopped for no reason. My desktop could ping but couldn't be pinged, not even on my lan.
I had reinstalled etc etc and then I noticed something really simple.
You need to make sure that everybodies network is set to home and not public. If it is public, then you will have tunneling problems. (This is with Windows 7).
So far it has fixed all of the problems we have had, as one of my mates also had his network set to public. Make sure that Hamachi is part of the homegroup and you should be ok.
Now I am not for a minute going to suggest it will fix everybodies problems, but it is something that has worked for us, and I really hope it helps some of you out.