[Dovecot] Dovecot IMAP Authentication issue with Vpopmail

[Arup]

Hello All,
i've configured a qmail server (for office) under Ubuntu 12.04 server
following this guide- http://www.connor.net.au/tutorials/qmail/qmaillite/
everything working just fine except dovecot IMAP. i've followed this
section for dovecot-
http://www.connor.net.au/tutorials/q...te/dovecot.php<http://www.connor.net.au/tutorials/qmail/qmaillite/dovecot.php>
but when i go to telnet 143 and try to login with username/password, it
failed and showing error:
** BYE Internal error occurred. Refer to server log for more
information.Connection closed by foreign host.*
i think there may be some authentication issue with vpopmail and dovecot.
POP and SMTP both working. but why not IMAP? i can't also use webmail (i.e.
squirrelmail) as it don't working with IMAP. it's showing- *connection
dropped by IMAP server *error while trying to login.
i'm looking forward to a solution here. any qmail+vpopmail expert here? plz
help.
Thanks in advance.

B/R