Network dies

We have two offices. Main office have windows 2000 domain. We have 20 workstations most of them are running Windows 2000 professional and others are running Windows 98. Branch office we have three computers. They will access Main office servers by VPN connection. We have application called point. To access point all workstions should be mapped to I:\POINT directory. If one workstation from branch office connected to Main office server. We don’t have any problem in main office. But if all the workstaions from branch office connected to Main office server, all the network in the main office hangs and we need to restart Linksys hub. What is the solution to this problem.