Export fails with DBMS_XMLGEN error

Running Oracle 9.2 on HP-UX 11i.

Export of a single table, or series of tables (using the TABLES param) works fine.

Exporting a schema (OWNER param) fails with:

EXP-00056: ORACLE error 19206 encountered
ORA-19206: Invalid value for query or REF CURSOR parameter
ORA-06512: at "SYS.DBMS_XMLGEN", line 83
ORA-06512: at "SYS.DBMS_METADATA", line 345
ORA-06512: at "SYS.DBMS_METADATA", line 410
ORA-06512: at "SYS.DBMS_METADATA", line 449
ORA-06512: at "SYS.DBMS_METADATA", line 1156
ORA-06512: at "SYS.DBMS_METADATA", line 1141
ORA-06512: at line 1
EXP-00000: Export terminated unsuccessfully

What has me stumped is that I have the same Oracle version running on another platform, without giving any hassles when using export. BTW catexp has been run on both at db creation. Exactly why is XML used..? The Oracle Utilities Manual does not mention anything about XML depedancies for export (or have I missed something?).

Oh yeah - in order to trace the error, I'm exporting a schema that has nothing except 1 or 2 standard tables (vachar2's and numbers - no LOB's, no UDT's and so on).

Any suggestions will be appreciated. Thanks.

--
Billy