Extended stats

Hi,

I'm trying to create extended stats as below and unable to do it when sum is used for both the statements,version 11203

select DBMS_STATS.CREATE_EXTENDED_STATS('USER','ACCTG_LN_PC','(sum(amount),sum(amount_base),sum(resource_quantity))') from dual;

exec dbms_stats.gather_table_stats('USER','ACCTG_LN_PC', method_opt =>'for all columns size skewonly for columns (sum(AMOUNT))');

*

ERROR at line 1:

ORA-20001: Error when processing extension -  group function is not allowed

Thanks