Problems with virtualmin mailman module

I'm trying to set up some mailing lists for my virtualmin pro hosts. Have had a mailman server running for some time in a GPL installation of Virtualmin but, in my licensed version, I don't seem to be able to add members to the list. I get the error:

"Failed to add list member : Add members to a list from the command line. Usage: add_members [options] listname Options: --regular-members-file=file -r file A file containing addresses of the members to be added, one address per line. This list of people become non-digest members. If file is -', read addresses from stdin. Note that -n/--non-digest-members-file are deprecated synonyms for this option. --digest-members-file=file -d file Similar to above, but these people become digest members. --welcome-msg= -w Set whether or not to send the list members a welcome message, overriding whatever the list'ssend_welcome_msg' setting is. --admin-notify= -a Set whether or not to send the list administrators a notification on the success/failure of these subscriptions, overriding whatever the list's admin_notify_mchanges' setting is. --nomail -n Set the newly added members mail delivery to disabled by admin. --help -h Print this help message and exit. listname The name of the Mailman list you are adding members to. It must already exist. You must supply at least one of -r and -d options. At most one of the files can be-'."

Installed Mailman from packages, configured the default list as instructed by the Mailman installer and then enabled the plugin in Virtualmin. Can enable mailman on a host, create a list within that host but, not add any members to it. Any suggestions?