I needed to add a new field to a feature class to act as a unique key, but when I run: fields = ['OID@', 'state', 'navkey'] ids = inspected_points #list of oid values oidfield = arcpy.Describe(points).OIDFieldName #reference to ObjectID field name where_clause_points = """{0} IN{1}""".format(arcpy.AddFieldDelimiters(points, oidfield),tuple(ids)) with arcpy.da.UpdateCursor(points, fields, where_clause_points) as cursor: I get the error: for row in cursor: RuntimeError: Attribute column not found [42S22:[Microsoft][ODBC Driver 13 for SQL Server][SQL Server]Invalid column name 'navkey'.] [db.DBO.lines_split][STATE_ID = 0] I have been able to add and write to other fields, so I'm not sure why this one is not working. I know the field is there and available: fields = arcpy.ListFields('lines_split') for field in fields: print(field.name) This produces: ProjectId SurveyId TechnicianUsername TimestampUTC GPSLatitude GPSLongitude GPSAccuracyInFeet GPSAltitudeInFeet Shape OBJECTID state NEAR_FID NEAR_DIST NEAR_X NEAR_Y navkey This field is just a text field. I just want to populate it with values, but cannot for some reason access it. The code above all works perfect if you remove the 'navkey' from the list of fields, but once you add it in it fails. Ultimately I am looking to create and populate a field to contain GUIDS and act as a unique key, since you cannot rely on ObjectID or GlobalID as they can change and CopyFeatures does not copy the same keys. I have the python code to generate GUIDS as a string, but I need access to this new field to populate them.