problem with default value

getting error during binding xsdfile to java objects:
default value '1' is not a valid value

<xsd>
.....
<xs:element name="TransportUnitCharacteristics">
<xs:complexType>
<xs:sequence>
<xs:element ref="TransportUnitCode" minOccurs="0"/>
<xs:element ref="TransportUnitMeasurements" minOccurs="0"/>
<xs:element ref="TransportUnitCount" minOccurs="0"/>
<xs:element ref="TransportUnitIdentifier" minOccurs="0" maxOccurs="unbounded"/>
<xs:element ref="TransportUnitText" minOccurs="0"/>
<xs:element ref="TransportUnitDetail" minOccurs="0"/>
</xs:sequence>
<xs:attribute name="TransportUnitType" type="transportUnitType" use="required"/>
<xs:attribute name="TransportUnitVariable" type="transportUnitVariable" use="optional"/>
<xs:attribute name="TransportUnitLevel" type="nni1" use="optional" default="1"/>
</xs:complexType>
</xs:element>
.....
<xs:simpleType name="nni1">
<xs:restriction base="xs:nonNegativeInteger">
<xs:totalDigits value="1"/>
</xs:restriction>
</xs:simpleType>
.....
</xsd>

this is a fragment of papiNet xml file