Can't add new mailboxes

[hfr]

Hello,

ISPConfig-Version 3.0.4.6
Linux: CentOS release 5.8 (Final) 32-Bit (setup According to "perfect server guide centos 5")

It is not possible to add new mailboxes anymore via ispconfig. Since I don't add mailboxes very often I am not sure when it stopped working, but 1-2 month ago it still worked.

In ispconfig gui everything seems ok (mailbox is added successfully), but when trying to login to roundcube or catching mails via imap the following error msgs are written to /var/log/maillog:

Dec 10 10:39:32 server imapd: Connection, ip=[::ffff:127.0.0.1]
Dec 10 10:39:32 server imapd: LOGIN, user=bb@domain.de, ip=[::ffff:127.0.0.1], port=[59956], protocol=IMAP
Dec 10 10:39:32 server imapd: Error reading ACLs for INBOX.sieve: No such file or directory

This only happens with new mailboxes, all existing mailboxes work.

Any ideas what can cause this?

Regards
Hans