VPN connection problem

I am using a Macbook 13" unibody. It's a late 08 model.

I just set up a vpn in office using a DrayTek 2950G vpn router connected to a Lenovo server. I can connect and access the shared files in the Lenovo server no problem when I am in office. But when I go home and try connecting with VPN, it doesn't work. It shows "connected", but after about 1 min, the connection drop. I tried to access the server before the connection dropped, but it doesn't work as well.

I tried connecting the VPN with my bro's PC running Win7 (also connected to the same router and network at home), and it works perfectly.

I then brought my Macbook out to some public wifi spot (tried 2 different public wifi) and it works.

I google this problem and some people suggested to check also "send all traffic over VPN connection" and "Use verbose logging" in the option tab inside the advance setting, but still no luck.

Anyone knows how to solve it?
Thanks for the help!

Edit: one more thing, I can remote the server desktop from home using the same network. It's just the VPN that doesn't work!

Edit (26 June, 2010): Tried last night again at home with my macbook, but instead of connecting internet through my Linksys router, I connect it directly to the modem and it works!!!! umm...

 

Anyone has similar problem? any suggestion may help. Thanks.

I forgot to try DMZ hosting last time and now the server is down for some reasons.. will try that later also..