You could check the permissions the users have, from what I remember the user that is used with the API should have admin permissions. For our API integration we normally create a local account in Orion for the application. However my AD admin account can use the SWQL studio.
Hope you have some luck getting this working.
the API user does not normally need admin privileges, unless you want to be able to execute some random piece of SQL.
I also use an local account with a very cryptic password for API access.