CI and server compatibility

[eluser]Whis[/eluser]
Before the PHP sessions,

I used the CI session, but my server just sent me that the request was too big (and the POST or GET array was too big). On another server, the request just stoped ...

Any Idea ? Thanks

EDIT: I also tested with a new copy of CI and just adding in it "session_start()" and i've the same issue... maybe something wrong in the server configuration ?