Single sign on don't work

Single sign on don't work

Hi
 
I'm trying to set up the ServiceDesk Plus
 
And would like to use the Single Sign on.
I've set it up and imported the users. But when they try to connect to the site http://servername:8080 they get a windows authentication pupop all the time....then if you type in your cridentials it just keeeps poping up until it times out. After that the deafailt logon page for Servicedesk plus shows.

                  New to ADSelfService Plus?