A 'snapshot too old' msg is received if the Oracle server can't construct a read-consistent image of data. This error is caused when the transaction that made the change has already committed and: the transaction slot in the rollback header has been reused or the before-image in the rollback segment has been overwritten by another transaction.

This problem can be minimized by ensuring the rollback segments are created with higher MINEXTENTS, larger extent sized, higher OPTIMAl value.