[Dovecot] Unable to access the mailbox or folders !!

[nasir nasir]

Hi all,
        I have installed dovecot on redhat linux with
ldap backend. I can login using ldap account in to my
webmail (squirrelmail) .But when I login to the
webmail , I cant see any inbox or anything . Just some
error messages like this ,

ERROR:
ERROR : Connection dropped by imap-server.
Query: LIST "" "Sent"

ERROR : Could not complete request.
Query: SELECT "INBOX"
Reason Given: 

I tried to telnet to port 143. Its also similar case.
It allows me to login but when I give "select" command
, it gives error(in fact, "NO" and nothing else). 

Required info,

OS - Redhat 8.0 
dovecot - dovecot-0.99.10-2.dag.src.rpm ( --with-ldap
--with-rawlog additionally)
MTA - Exim 4.14
Webmail - Squirrelmail 1.4.1-2
Location of Maildir - /var/spool/mail/USERNAME/Maildir
dovecot configuration has the following line,

default_mail_env = maildir:/var/spool/mail/%u/Maildir

Is there anything I am missing or doing wrong ? I am
sorry if this is a silly question. But I am a newbie
to dovecot and did a lot of google search for this
error  or even additional documentation for dovecot
without any success. Any suggestion or advice would be
highly appreciated.
Regards,
Nasirudheen

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