To stay logged in, two things have to occur;
1. the user's browser has to accept cookies.
2. the script has to be able to write a file in the /calendarscript/session/ directory.One of those things must not be occurring. 
BTW. Some users reported log-in problems when they exceeded their server disc space quota, preventing the session file from being created.
JFYI
Dan O.
www.much2.com