Its very easy to simulate this error.

If I know what kind of operations are happening, I can demonstrate this error irrespective of rollback segment size and number of rollback segments.

ORA-1555 is probably the most discussed oracle error on the Net. You can find it at quite a few places that ORACLE's error message for this number is mis-leading.

Its also known that howsoever huge rollbacks you create, you can not gurantee that this error will not occur during export if data changes are happening simultaneously.