Multiple VPN Connections on a DLink 624 Wireless Router

Hi All,
I have recenly purchased a DLINK 624 wireless Router. I am using it with a Cable Internet Service.
I am trying to connect to my office’s VPN using the router.
The problem is if anyone else is connected to the VPN using the same router the moment I try to connect the existing connection gets disconnected.
I tried to google this issue but was unsuccessfull.
Can anyone please guide me how to establish multiple VPN sessions concurrently using the same router?
–
Chandu