After some users reporting their inability to connect to Endian UTM Appliance via IPsec/L2TP using their Android devices, our investigations led to the discovery of the following bug in Android ICS 4.X.X. Basically, Android sends malformed packets to the IPsec tunnel, preventing the connection to the Endian UTM Appliance. At the moment, there is a patch for users of Openswan (source code diff here).
This bug does not affect older versions of Android. We will keep you informed about the resolution of this bug.
Thanks to all users that reported this problem allowing us to investigate!