CI Sessions - No user data

[eluser]DougW[/eluser]
I have just experienced a similar problem. I have several sites, all of which work. I have a 'Generic controller from which all other controllers are spawned, except for login. Login logs a user in and if I break and print the session, all my session variables are there. But after login in I redirect to the homepage which starts at the Generic controller. When I dump the session there, no userdata. It has dropped it. The sites are just different enough that it is difficult to compare them. What I am looking for is suggestions for what types of things can cause a session to get dropped. As I say, I have many other sites where this works on the same server with the same installation of CI. it is so weird to have one just drop the variables. I am using database and have double checked all the table names, field names, even the collation as there was some discussion on that a while back. Any ideas?