OK - we may need a bit more information to be able to help.
As you probably know, the iPad VPN supporting the L2TP, PPTP, or Cisco IPSec VPN protocols.
Just to check, I guess you've done the following.
Configure VPN
Tap Settings > General > Network > VPN > Add VPN Configuration. Then use the VPN settings for your device.
* Server = your computer's external IP or hostname.
* Account = your account login
* RSA SecurID = OFF
* Password = your account password
* Secret = computer's secret, chosen during set-up.
* Send all traffic = ON
Turn VPN on or off
If you have created a VPN configuration, you would find the option to turn VPN on or off in the Settings.
First disable Wi-Fi on iPad, then start VPN in the settings. Wait until it finishes connecting and the status bar would has the VPN icon.
Note: iPad will drop VPN whenever changing the networks.
You say that this worked OK on your iPad1 but fails on the iPad2. Does it just fail to connect or is there some other issue?
Have you tried the 'cure all' fix of turning the iPad completely off then on again - i.e. by holding down the Power button?
Get back to us with some more information and hopefully we'll come up with some more ideas...
Tim