Navision 3.7 running on SQL, error when attempting add field

pault

User has loaded his development license,
goes to Tools, Object Designer, selects table 38 Purchase Header, adds a new field with ID 8000, named as Our Sales Ref, type character, length 30.
Attempts to commit this change by closing the window and we get a permission error:

The following SQL error has occurred
3704 and 42000
User does not have permission to perform this action.
The user is set up as role "SUPER" within Navision. We are using Windows authentication.

Where do I set permissions to allow the user to make changes to tables?

DenSter

Try using field number 50000 or higher.

Also, the user must be dbo for the Navision database on SQL server.