I am POSTing a new user request and when I choose the 'Salesforce' profileId, I get 'license limit exceeded'.  However I can create that same user with the 'Chatter Free' profile ID.  I have reviewed my company info and see that I still have 18 licenses available under Salesforce.  On the edit page for that profile, I have enabled the access for my connected app, and it is api-enabled.  So what else is needed?