Ipsec/l2tp VPN using windows XP xlient

I have setup the IPSEC/l2tp VPN using the certificate authentication & generate policy=yes.

It is working well but the dynamic policy is not getting deleted even after client disconnect.

Some time new client is not able to establish the IPSEC communication , if i restart the routerboard that same client is able to connect

Please suggest me

1 .how we can delete the dynamic policy
2. I suspect this due to the dynamic policy only where new clients are not able to connect , if not can anyone suggest me the probable reason

Regagrds

Porush