If you try to create a calendar on a designated back-end machine, and you get the following error message: Invalid DWP Host Server. it means one of two things. Either your server is not configured properly, or the calendar owner has already been assigned to a different back-end server.
Look at the ics.conf file for the back-end server in question. Verify that the following settings exist:
service.dwp.enable = "yes" caldb.cld.type = "directory" local.hostname = "back-end hostname"
Look at the user's LDAP entry and see if there is an icsDWPHost attribute present. The value of icsDWPHost must match the back—end server name on which you are attempting to create the calendar. You can not create a calendar for this user on a different back-end server.