I ran into a pretty frustrating problem trying to set up L2TP on my iphone. I followed the instructions on the site, entering all the information as it was presented, but for some reason the password and secret fields reset to blank after I save the configuration settings. turning on the VPN at that point brings up a screen asking me for the password. when I enter the password, i get the following message:
"The IPSec Shared Secret is missing. Verify your settings and try reconnecting."
At that point I hadn't touched any settings under the IPSec tab, so I entered the shared secret/key in the Secret field under the IPSec tab. Trying to turn on the VPN after this doesn't bring up the password prompt, just this message:
"No VPN shared secret was provided".
Any idea what's causing this behavior? I'm on an iphone 4 with 5.0.1 if that makes a difference.