I am setting up a windows2003 server as a VPN Server. When I try to connect from a Windows XP system over a Dial up modem everything works fine. However when I try to connect from behind a Broadband router I get the following error Error 788: The L2TP connection attempt failed because the security layer could not negotiate compitable parameters with the remote computer.
I am using a preshared secret instead of a certificate. PPTP works fine even behind the nat device. Ahy ideas what the problem could be?