If you use the options link to disable a user, sometimes they are not removed from the mailing list.

The thing to do is to check that the root user can list users. Do:

 su - root
 /export/home/mailman_1/bin/find_member cxbrooks@gmail.com
You should the mailing lists to which the user belongs. If you don't, then there are problems with the mailman or the path of the root user I had to create a link:
ln -s /usr/local/bin/python /usr/bin