L2TP not working using windows dial up on XP windows client

cahmadh

hi,
I have configured the Juniper ssg-140 for site to site VPN and client VPN. The problem is when i installed the netscreen client on the windows xp system then only the i am able to connect to the VPN using my windows XP VPN dial up. If i'll not installed the Netscreen on the system and try to connect with simply windows XP client it does not work?

Why is this so? Do i need to add some certificates in XP?
My VPN is policy based and i am using L2TP IP Sec.