Hi, folks!
There is Roundcube 0.2.1 (seems that 0.3.1 has this problem too).
Mailboxes are IMAP under Dovecot.
There are two folders visible: Inbox and Trash,
but when I try to remove message,
"errormoving" alert is displayed, and "Trash" is always empty.

File roundcubemail/program/include/rcube_imap.php contains following code:

  function move_message($uids, $to_mbox, $from_mbox='') 
    { 
    $to_mbox = $this->_mod_mailbox($to_mbox); 
    $from_mbox = $from_mbox ? $this->_mod_mailbox($from_mbox) : $this->mailbox;

    // make sure mailbox exists 
    if ($to_mbox != 'INBOX' && !in_array($to_mbox, $this->_list_mailboxes())) 
      { 
      if (in_array($to_mbox_in, $this->default_folders)) 
        $this->create_mailbox($to_mbox_in, TRUE); 
      else 
        return FALSE;   // This always happens when Trash does not exists!
      }

What is $to_mbox_in variable in this code?
It is never assigned and is always empty (while $to_mbox == 'Trash').

BTW, when Trash folder is already created, then messages are removed normally,
but two "Trash" folders are visible in folderlist.

WBR, Ilya