Help: error message ORA-06554, why?

I run a PL/SQL like below:

Create Or Replace Function GetExamNo (pExam_date in date,pSick_cal......

.................

but SQL/PLUS return a error message like below:

ORA-06554: package DBMS_STANDARD must be created before using PL/SQL.

but I had been run the SQL script DBMSSTDX.SQL, Can anyone tell me why have the error message?

Thank's! Received on Sun Feb 02 1997 - 00:00:00 CST