Service tiers Credential Type is using Access Control Service
Problem
Can't login with users regular username/password.
Solution
Authentication type of the user, and whether you require a Web Service Access Key will depend on the Credential Type of your service tier.
If you're using Access Control Service (ACS), you will need to generate a web service access key and use that in the client application that is accessing the NAV data.
For the Windows Credential type, a regular username/password combo will do, though you can choose between a Windows user or a NAV user.