Cannot delete folders from Maildir in only one account

Hi

I try to delete the folder „test" from Thunderbird 31.4.0 (Win), Webmail (Sogo 2.2.16), or Mail 8.2 (Mac Yosemite), but I am not able to delete in this account. Nevertheless I am able to create new folders. These new folders are not deleteable, too.

dovecot 2.2.9 on Ubuntu 14.04 LTS 64-bit

In /var/log/mail.{err,log} I cannot see any errors.

In another account it works without any problems. (create and delete folders)

Have you any hint, I can try?

Chris