iPad VPN fails to connect on iOS 4.2.1

After installed iOS4.2 on my iPad, I use configuration profiles to setup my VPN settings and it currently connects to a SonicWall VPN using L2TP. Then the VPN connection is breaken, but it definitively worked under 3.1.3. I have reinstalled my Profile on iOS4 but still nothing. Why the VPN fails to connect?This is a original bug. After I changes encryption from 3DES to AES-128, the issue seems to