Hello Tony, it looks like some extra filter in the chat configuration is enabled. If you have the 'Filter by firendship' enabled ensure that the 2 users have a confirmed firendship in Jomsocial and also that there are no other filters activated for access level, live support mode, etc

Of course ensure that without any filters you are able to see the side list of users correctly.

The private messaging list normally lists all registered users.

John