This error suggests that you have no more free licences on your Sugar Connect subscription. If you are a Sugar Connect admin then do the following to check your subscription:
Find the Sugar Connect option in the outlook toolbar
Choose Open Sidebar
On the Sidebar click the Settings cog
Select Open Sugar Connect Portal
Compare the number of users on the Users tab with the Number of Licences on the Subscription tab
You will either need to remove a user as necessary to add new users