[Dovecot] Virtual Folder configuration problem.

I'm attempting to create a virtual inbox that contains all unread
messages from the user's Maildir.

I created a conf file called 80-virtual.conf containing:

mail_plugins = $mail_plugins virtual

namespace { prefix = virtual/ separator = / location = virtual:~/Maildir/virtual }

And created the

/home/username/Maildir/virtual/unseen/dovecot-virtual file which contains:

# ~/Maildir/virtual/unseen/dovecot-virtual * unseen

However it doesn't work and the maillog file contains:

dovecot: imap(username): Error: user username: Initialization failed:
namespace configuration error: inbox=yes namespace missing

This is with dovecot 2.0.beta6 (3156315704ef)

Does anybody have any suggestions?

Thanks!

Terry