[binc] Squirrelmail and Binc IMAP

I will be moving accounts from a Courier server to a new server which  
I'm going to try Binc on, so I've configured Binc to use Maildir++.  
After a succesful login via Squirrelmail I get the following error:

ERROR : Could not complete request.
Query: CREATE "INBOX.Sent"
Reason Given: CREATE failed: invalid mailbox name

I've configure Squirrelmail to user the Courier configuration. Is  
there something that I need to do to make Squirrelmail work with Binc?

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Regards, Charles.