ORA-01591: lock held by in-doubt distributed transaction

 We have a transparent gateway to a SQL Server database.  When I try to do a SELECT from one of the remote tables I'm getting the error message :

ORA-01591: lock held by in-doubt distributed transaction 8.42.76256

I've tried

SELECT * FROM dba_2pc_pending
              *
ERROR at line 1:
ORA-00942: table or view does not exist

and also

SQL> SELECT local_tran_id
  2  ,state
  3  ,status
  4  FROM sys.pending_trans$;
FROM sys.pending_trans$
         *
ERROR at line 4:
ORA-00942: table or view does not exist

in desperation I have tried using both

ROLLBACK FORCE '8.42.76256'

and

COMMIT FORCE  '8.42.76256'

Can anyone suggest how to remove the in-doubt transaction.