I am sure many of us must have faced this issue.Problem:My flat file schema has an optional  record  and marked with a tagidentifier. we would think that the input message without that optional record will pass the schema validation. But by default Biztalk throws an error about the missing record if we try to 'Validate the instance' in the Biztalk mapper.Resolution:On the schema node, set Parser Optimization to “Complexity” instead of thedefault "Speed" optimization.