VPN

Sorry guys im new to this, basically i have set up a standard windows VPN connection between two offices, using windows XP sp2 on client machines and SBS2003 as the server software, when i want to dial into the main office it allows me, authenticates, can access emails and shared drives, but when someone else tries to connect in the same office it wont let them or kicks the client machine already accessing the VPN connection PLEASE HELP IM BEGGING