@morrow without logs this will be hard to track down. can you ask your administrator to open up a support case for this?
Webmin is a webbased tool for server administration.
When using Zarafa with a LDAP server, it's easy to administrate users over Webmin. The intregration shows you how to modify the webmin configuration to set Zarafa specific settings using the LDAP-Manager for webmin.
Easy management of users using Webmin.