[Dovecot] IPhone wont delete IMAP messages from dovecot mailbox

[tibby at tibby.hu]

Hello!
I've got dovecot running with postfix. Have virtual users under vmail 
folder.
When I connect with outlook, I can read, delete messages.
When I sign on with webmail, also can delete messages,
Mutt is working as well on the mail server, can delete messages.

Once the message is deleted it moves  to the trash. Works as it 
supposed to.

But on Iphone, when I add a mail user, got the mailbox synced with IMAP 
I can see the INBOX, but when I delete a message, get this error:
"Unable to Move Message The message could not be moved to the mailbox 
Trash."

http://www.netchimp.co.uk/webdesign/wp-content/uploads/2011/12/iphone_unable_to_move_message.png

What causing this problem?
Please Help.