ASC comes with an own IPsec service. To start this service, ASC disabled the default windows ipsec service. It's not possible to run windows's IPsec service and ASC's IPsec service at the same time. To make L2TP work again, you have to disable the services of ASC (called "ncprwsnt" and "NcpSec") and enable the windows ipsec service (called "ipsec").