I changed it to 'db' but no luck.
Same problem, when I type the login and the password, I'm returned to the login screen again.
I see a IMAP login in my hmailserver logs, but directly I see also a logout...
(there is also a thread about this). Don't know if this is the cause....
There are other threads talking about session issues, with the php session.auto_start = 0, but also no luck...