something very wierd - only one user from many on the server can't save message to sent or draft. all others - can.
the error from the log:
[10-Oct-2013 08:59:08 +0000]: IMAP Error: Could not save message in INBOX.Sent in /mnt/must/roundcube/roundcubemail-0.9.3/program/steps/mail/sendmail.inc on line 779 (POST /webmail/?_unlock=loading1381395550257&_lang=en?_task=mail&_action=send)
[10-Oct-2013 09:01:36 +0000]: IMAP Error: Could not save message in INBOX.Sent in /mnt/must/roundcube/roundcubemail-0.9.3/program/steps/mail/sendmail.inc on line 779 (POST /webmail/?_unlock=loading1381395698245&_lang=en?_task=mail&_action=send)
[10-Oct-2013 09:04:47 +0000]: IMAP Error: Could not save message in INBOX.Sent in /mnt/must/roundcube/roundcubemail-0.9.3/program/steps/mail/sendmail.inc on line 779 (POST /webmail/?_unlock=loading1381395888879&_lang=en?_task=mail&_action=send)
[10-Oct-2013 09:08:58 +0000]: IMAP Error: Could not save message in INBOX.Sent in /mnt/must/roundcube/roundcubemail-0.9.3/program/steps/mail/sendmail.inc on line 779 (POST /webmail/?_unlock=loading1381396140576&_lang=en?_task=mail&_action=send)
[10-Oct-2013 09:10:05 +0000]: IMAP Error: Could not save message in INBOX.Sent in /mnt/must/roundcube/roundcubemail-0.9.3/program/steps/mail/sendmail.inc on line 779 (POST /webmail/?_unlock=loading1381396206097&_lang=en?_task=mail&_action=send)
[10-Oct-2013 09:10:44 +0000]: IMAP Error: Could not save message in INBOX.Drafts in /mnt/must/roundcube/roundcubemail-0.9.3/program/steps/mail/sendmail.inc on line 779 (POST /webmail/?_unlock=loading1381396246748&_lang=en?_task=mail&_action=send)
[10-Oct-2013 09:11:24 +0000]: IMAP Error: Could not save message in INBOX.Drafts in /mnt/must/roundcube/roundcubemail-0.9.3/program/steps/mail/sendmail.inc on line 779 (POST /webmail/?_unlock=loading1381396286815&_lang=en?_task=mail&_action=send)
[10-Oct-2013 09:12:26 +0000]: IMAP Error: Could not save message in INBOX.Drafts in /mnt/must/roundcube/roundcubemail-0.9.3/program/steps/mail/sendmail.inc on line 779 (POST /webmail/?_unlock=loading1381396348469&_lang=en?_task=mail&_action=send)
[10-Oct-2013 09:13:27 +0000]: IMAP Error: Could not save message in INBOX.Drafts in /mnt/must/roundcube/roundcubemail-0.9.3/program/steps/mail/sendmail.inc on line 779 (POST /webmail/?_unlock=loading1381396409469&_lang=en?_task=mail&_action=send)
[10-Oct-2013 09:14:28 +0000]: IMAP Error: Could not save message in INBOX.Drafts in /mnt/must/roundcube/roundcubemail-0.9.3/program/steps/mail/sendmail.inc on line 779 (POST /webmail/?_unlock=loading1381396470468&_lang=en?_task=mail&_action=send)
