WINDOWS 2000 VPN PROBLEM

I am the IT Personnel of Steelscreen Limited, London ofice with 15 users. We have just installed Watchguard SOHO Internet Security on our office Network (Using a 2MB leased line) in London using Windows 2000 VPN to connect to our VPN Server running Windows 2000 Server in Stockholm. Since this installation, I find out that users sometimes have to relaunch their VPN connection in order to send & receive email and browsing is never a problem.
I have checked the configuration and everything is correct.
Can you help?