When one submit an user group with external user groups, and this doesn't work for whatever reason, like:

Net::LDAP::Error - No route to host - connect(2)
LdapFluff::Generic::UnauthenticatedException
LdapFluff::ActiveDirectory::MemberService::UIDNotFoundException,

it should show these errors in the UI and ideally some text explaining how to solve the issue.
Currently the errors are merely logged to production.log, which leaves users unable to understand what happened.