SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE    10.2.0.1.0      Production
TNS for Linux: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production

SQL> select dbms_metadata.get_ddl('TABLE','OSM_DML_10','OSM_TAB_4') from dual
  2  /
ERROR:
ORA-31603: object "OSM_DML_10" of type TABLE not found in schema "OSM_TAB_4"
ORA-06512: at "SYS.DBMS_METADATA", line 1546
ORA-06512: at "SYS.DBMS_METADATA", line 1583
ORA-06512: at "SYS.DBMS_METADATA", line 1901
ORA-06512: at "SYS.DBMS_METADATA", line 2792
ORA-06512: at "SYS.DBMS_METADATA", line 4333
ORA-06512: at line 1

no rows selected

在Metalink找的结果：
Applies to:

Oracle Server - Enterprise Edition - Version: 9.2.0.0 to 9.2.0.8
This problem can occur on any platform.

Symptoms
Execution of dbms_metadata.get_ddl results in ORA-19206,ORA-6512

e.g.
SQL> select dbms_metadata.get_ddl('TABLE','TEST') from dual;
ERROR:
ORA-19206: Invalid value for query or REF CURSOR parameter
ORA-6512: at "SYS.DBMS_XMLGEN", line 83
ORA-6512: at "SYS.DBMS_METADATA", line 345
ORA-6512: at "SYS.DBMS_METADATA", line 410
ORA-6512: at "SYS.DBMS_METADATA", line 449
ORA-6512: at "SYS.DBMS_METADATA", line 615
ORA-6512: at "SYS.DBMS_METADATA", line 1221
ORA-6512: at line 1

Cause
This error may occur if either XML Database in not installed or has not been installed properly.

Solution
Reinstall XML Database (XDB)