ora-01466 unable to read data - table definition has changed

I run a select with flasback query and is produced error ORA-01466, but the table definition has not changed.

The select is:

select * from "owner.table_name" as of timestamp to_timestamp('15-02-2012 10:40','DD-MM-YYYY HH24:MI');

If the "of timestamp to_timestamp" is in the interval of 5 to 55 minutes then the select it's Ok.
But if the "of timestamp to_timestamp" is greater then 55 or 60 minutos then the select generated ORA-01466.

Why is generated the ORA-01466?

Today, I see the values of the rows in the SMON_SCN_TIME table and are not correct.
The table have values of October 2011 and May 2030.