Why do I got ORA-00904 invalid identifier when running a simple query?

Using DB 11.2.0.1 on linux x86
Just run a query as follows:

select USER_NAME, ora_rowscn from fnd_user_preferences ;
select USER_NAME, ora_rowscn from fnd_user_preferences
                 *
ERROR at line 1:
ORA-00904: "ORA_ROWSCN": invalid identifier

yet this works?
select DUMMY
,      ora_rowscn
from dual ;

D ORA_ROWSCN
- ----------
X 5.9843E+12