[Dovecot] Converting from Maildir to dbox

Hi,

How do i convert from Maildir to dbox using the convert plugin?

My users reside in /home/user/Maildir.

In the dovecot.conf file i've set up

convert_mail = dbox:%h

but I am not sure about the syntax. Im getting the error:

Couldn't create mailbox directory INBOX Mailbox conversion failed, exiting

Thanks

-- Kjartan