If your RoamNet connection is idle for 5 minutes (approximately) the Cisco Systems VPN Client terminates the VPN tunnel. Subsequent re-authetication is required. This is a known issue with the Windows Vista Firewall * blocking ISAKMP messages.

INSTRUCTIONS: Copy & Paste the following commands into a Command Console with elevated Administration privileges.

@echo off
netsh advfirewall firewall delete rule name="UCL RoamNet Cisco VPN ISAKMP"
netsh advfirewall firewall add rule name="UCL RoamNet Cisco VPN ISAKMP" 
  dir=in program="%PROGRAMFILES%\Cisco Systems\VPN client\cvpnd.exe" 
  localport=500 remoteport=500 protocol=UDP remoteip=128.40.255.64/29 
  action=allow
netsh advfirewall firewall show rule name="UCL RoamNet Cisco VPN ISAKMP"
pause

* This is regardless of the Windows built-in Firewall statues. Even if a 
3rd party firewall (e.g. FSecure, Norton, AVG) is installed and the 
built-in firewall is disabled the firewall rules still apply. 

This issue may also apply to Windows 7