You cannot connect a computer that is running Windows Vista to a Cisco ASA Series VPN server by using a virtual private network (VPN) connection that is based on the “Layer 2 Tunneling Protocol with IPsec” (L2TP/IPsec) protocol. This problem occurs if another Windows Vista-based computer is already connecting to the VPN server through a L2TP/IPsec-based VPN connection. You cannot connect to the VPN server until the other computer disconnects from the VPN server.

This behavior does not occur on a computer that is running Windows XP or Windows Server 2003.