Ever since I upgraded to Snow Leopard I've had a problem with VPN. I connect and all is well for 30 minutes or so. Then it just stops. The clock continues to run but no data is exchanged. I disconnect, wait 30 seconds and then all is well for another 30 minutes. Here's what I have done with no success:

Deleted and reinstalled the VPN

Deleted the Network interface Plist

Also at this time I installed a new router.

None of this has had any effect on the situation. Any suggestion or guidance that points me towards solving this problem would be much appreciated.