dsync error: Can't sync mailbox tmp: Mailbox isn't selectable

Hi,

I am trying to use dsync to migrate from mbox to Maildir with

dovecot --version 2.2.27 ()

The configuration seems to be working and some of the mailbox can be mirrored via

dsync -u username mirror mbox:/home/username/mail:INBOX=/var/mail/username

I have trouble with one user where I get the error.

dsync(username2): Error: Can't sync mailbox tmp: Mailbox isn't selectable

Any ideas where to look for hints?

Regards

Hagen Bauer