Incorrect SQL query (oracle) for subquery

[baxster]

I tried this query:

        var states =
            from fts in DataContext.GetTable<FirmToState>()
            orderby fts.StateChangeDate descending
            select fts;

        var query =
            from f in DataContext.GetTable<Firm>()
            select new
            {
                FirmID = (long?)f.ID,
                StateID = states.Where(s => s.FirmID == f.ID)
                                .Select(s => (long?)s.StateID)
                                .FirstOrDefault(),
            };

Classes of metadata:

    public class FirmToState
    {
        public DateTime StateChangeDate { get; set; }
        public long FirmID { get; set; }
        public long StateID { get; set; }
    }

    public class Firm
    {
        public long ID { get; set; }
    }

query formatted in oracle as:

SELECT 
f.ID, 
( 
    SELECT tn11.* 
-- should be: SELECT tn11.STATE_ID
    FROM 
    ( 
        SELECT tn1.*, ROWNUM as rnn1 
        FROM 
        ( 
            SELECT 
                s.STATE_ID 
            FROM 
                VFIRM_TO_STATES s 
            WHERE 
                s.FIRM_ID = f.ID 
            ORDER BY 
                s.STATE_CHANGE_DATE DESC 
        ) tn1 
    ) tn11 
    WHERE 
        tn11.rnn1 <= 1 
) as c1 
FROM 
VFIRMS f 

Oracle reports error ORA-00913: too many values When "SELECT tn11.*" is replaced with "SELECT tn11.STATE_ID" , the query executes without errors.