exp username/password file=xxxx.dmp  log=xxx.log tables=table_nameflashback_scn=xxxxxx 时

报错 exp-00008 ora-01466 exp-00000

scn:

select dbms_flashback.GET_SYSTEM_CHANGE_NUMBER from dual;

单独执行：

select count(1) from username.table_name as of scn xxxxx;

同样报错ora-01466

请问怎么样查找ora-01466的原因 

官方解释：

ORA-01466: unable to read data - table definition has changed

Cause: Query parsed after tbl (or index) change, and executed w/old snapshot

Action: commit (or rollback) transaction, and re-execute