Insufficient privilege when creating an index in Oracle 11g

I am trying to create an index in Oracle, my ddl :

create index OMD_DOCTEXT2_CTX on table_name(col_name)
indextype is ctxsys.开发者_运维知识库context local
parameters ('datastore CTXSYS.FILE_DATASTORE filter ctxsys.null_filter  lexer E2LEX wordlist E2WORDLIST stoplist E2STOP section group E2GROUP') parallel 4;

I am getting error :

ORA-29855: error occurred in the execution of ODCIINDEXCREATE routine
ORA-20000: Oracle Text error:
DRG-10758: index owner does not have the privilege to use file or URL datastore
ORA-06512: at "CTXSYS.DRUE", line 160
ORA-06512: at "CTXSYS.TEXTINDEXMETHODS", line 366

Any ideas?

From the Oracle Text Documentation:

File and URL datastores enable access to files on the actual database disk. This may be undesirable when security is an issue since any user can browse the file system that is accessible to the Oracle user. The FILE_ACCESS_ROLE system parameter can be used to set the name of a database role that is authorized to create an index using FILE or URL datastores. If set, any user attempting to create an index using FILE or URL datastores must have this role, or the index creation will fail.

For example, the following statement sets the name of the database role:

ctx_adm.set_parameter('FILE_ACCESS_ROLE','TOPCAT');

where TOPCAT is the role that is authorized to create an index on a file or URL datastore. The CREATE INDEX operation will fail when a user that does not have an authorized role tries to create an index on a file or URL datastore.

So, does your user have the necessary role?