Cannot add site member , "no users found"

Dear All,

This is my first install on Alfresco, we use Alfresco community ed. 5.0.d.

After creating a site, I also create users and groups, then I try to add site member.

But any user name or group name that I type, always get the message : "No users found" or "No groups found",
Is there any step that I miss here ?

(I have read the docs, and seems that I should be able to add site member at this stage)

Many thanks for your help,
Regards
Krist