I just checked that (after reading your reply), every user I tried has this role - I am using the samples (users, roles, ...), so "Alex Pink", "Rye Woodard" and "Tony Blue" do have the "Workspace-User" role.
Checking the users in the adminui, I found that there weren't any even though I could log in to the adminui as one. Also, the drop list that allows you to restrict the search to a specific domain contained none of our domains or even the default domain.
I went to domain management and changed the name of the default domain just to force a write to the database. After doing this, everything started working normally.
If you can log into the Admin UI as the "administrator" user then you should be able to log into workspace too. If you are trying to log into workspace as any other user identity, then make sure that the user has the appropriate permission; for example try assigning the "Workspace User" role to that user in the Admin UI.
If you cannot even log on to Workspace as the "administrator" user then chances are something is wrong with your installation. You should have a look in the server log to see if there is any error being reported.