dbms_metadata.get_ddl materialized view

 SEVERE 56           80813    oracle.dbtools.db.DBUtil

ORA-31603: object "objectname" of type MATERIALIZED_VIEW not found in schema "schema name"

ORA-06512: at "SYS.DBMS_SYS_ERROR", line 105

ORA-06512: at "SYS.DBMS_METADATA", line 3912

ORA-06512: at "SYS.DBMS_METADATA", line 5678

ORA-06512: at line 1.

I am getting this error while

select dbms_metadata.get_ddl('MATERIALIZED_VIEW','obejct_name','schema') from dual;

, I have recently upgraded from 10.2.0.3 to 11gr2. I have missed to stop the materialized view refresh before upgrade. This i have done on test server.

Please let me know how i can resolve this issue.