Fields where 'type' attribute has value 'MULTIPLESTRINGVALUE' are referenced in all FIX5+.xml. They cannot be correctly identified when added to DataDictonary because corresponding definition quickfix.FieldType ( quickfix.FieldType#MultipleValueString) expects value 'MULTIPLEVALUESTRING'.

Quick workaround for 1.6.1 is to update values in your xml dictionary, or change type to STRING and validate within app (as suggested elsewhere https://github.com/connamara/quickfixn/issues/66).

Proper fix would probably involve correcting both xml files and quickfix.FieldType to refer to MultipleStringValue constant as defined in the the official fixmlschema doc:

<xs:simpleType name="MultipleStringValue">
      <xs:annotation>
         <xs:documentation>string field containing one or more space delimited multiple character values (e.g. |277=AV AN A| ).</xs:documentation>
      </xs:annotation>
      <xs:restriction base="xs:string">
         <xs:pattern value=".+(\s.+)*"/>
      </xs:restriction>
   </xs:simpleType>

I would also suggest an engine to generate a warning (or allow some other strategy) when a DataDictionary parser encounters some 'unexpected' value (instead of just silently assuming type was Unknown)