An Oracle View, why it was invalid?

Dear Oracle,

Please advise, why did I get the view as invalid?

The select statement on SQLPlus is fine.

User: my_DBA_user, is a DBA user in Oracle 10g database.

Thanks

Liz

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CREATE OR REPLACE FORCE VIEW "my_DBA_user"."DBA_USER_PRIVS" ("USERNAME", "ROLENAME", "PRIVILEGE") AS

SELECT DECODE (sa1.grantee#, 1, 'PUBLIC', u1.NAME),                    

               SUBSTR (u2.NAME, 1, 20),           

               SUBSTR (spm.NAME, 1, 27)

FROM SYS.sysauth$ sa1,            

            SYS.sysauth$ sa2,         

            SYS.user$ u1,         

            SYS.user$ u2,         

            SYS.system_privilege_map spm

WHERE sa1.grantee# = u1.user#      

      AND sa1.privilege# = u2.user# 

      AND u2.user# = sa2.grantee#      

      AND sa2.privilege# = spm.PRIVILEGE

UNION