session cookie

well, this is a little conveluded in my description of my issue. I have one par of ltms 9.4 running a web site https://www.blah.com. These hit an Iplanet reverse proxy, that send the request to a second pair of ltms 9.4 to the internal web site https://www2.blah.com running asp.net 2.0.when I hit the internal site directly it appears to work fine but coming through the reverse proxy the session info is lost. this causes errors with in the app as you could imagine. So what I need is some way a user can persist to the same seesion on the back end.On the back end the cookie persistance appears to work fine.any insight would be greatly appreciated.The error is a "mac field failed"