Create a class c # from an xsd

I have a problem generating a class from an xsd.

the xsd

<?xml version="1.0" encoding="UTF-8"?>
<!--
  Library:           OASIS Universal Business Language (UBL) 2.1 OS
                     http://docs.oasis-open.org/ubl/os-UBL-2.1/
  Release Date:      04 November 2013
  Module:            xsdrt/maindoc/UBL-Invoice-2.1.xsd
  Generated on:      2013-10-31 17:17z
  Copyright (c) OASIS Open 2013. All Rights Reserved.
-->
<xsd:schema xmlns="urn:oasis:names:specification:ubl:schema:xsd:Invoice-2"
            xmlns:cac="urn:oasis:names:specification:ubl:schema:xsd:CommonAggregateComponents-2"
            xmlns:cbc="urn:oasis:names:specification:ubl:schema:xsd:CommonBasicComponents-2"
            xmlns:ext="urn:oasis:names:specification:ubl:schema:xsd:CommonExtensionComponents-2"
            xmlns:xsd="http://www.w3.org/2001/XMLSchema"
            xmlns:ds="http://www.w3.org/2000/09/xmldsig"
            targetNamespace="urn:oasis:names:specification:ubl:schema:xsd:Invoice-2"
            elementFormDefault="qualified"
            attributeFormDefault="unqualified"
            version="2.1">
  <xsd:import namespace="urn:oasis:names:specification:ubl:schema:xsd:CommonAggregateComponents-2"
                schemaLocation="https://docs.oasis-open.org/ubl/cs1-UBL-2.1/xsd/common/UBL-CommonAggregateComponents-2.1.xsd"/>
  <xsd:import namespace="urn:oasis:names:specification:ubl:schema:xsd:CommonBasicComponents-2"
              schemaLocation="https://docs.oasis-open.org/ubl/cs1-UBL-2.1/xsd/common/UBL-CommonBasicComponents-2.1.xsd"/>
  <xsd:import namespace="urn:oasis:names:specification:ubl:schema:xsd:CommonExtensionComponents-2"
              schemaLocation="https://docs.oasis-open.org/ubl/cs1-UBL-2.1/xsd/common/UBL-CommonExtensionComponents-2.1.xsd"/>
  <xsd:import namespace = "http://www.w3.org/2000/09/xmldsig" schemaLocation = "https://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/common/UBL-xmldsig-core-schema-2.1.xsd" />
   <xsd:element name="Invoice" type="InvoiceType"/>
   <xsd:complexType name="InvoiceType">
      <xsd:sequence>
         <xsd:element ref="cbc:UBLVersionID" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:CustomizationID" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:ProfileID" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:ProfileExecutionID" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:ID" minOccurs="1" maxOccurs="1"/>
         <xsd:element ref="cbc:CopyIndicator" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:UUID" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:IssueDate" minOccurs="1" maxOccurs="1"/>
         <xsd:element ref="cbc:IssueTime" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:DueDate" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:InvoiceTypeCode" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:Note" minOccurs="0" maxOccurs="unbounded"/>
         <xsd:element ref="cbc:TaxPointDate" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:DocumentCurrencyCode" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:TaxCurrencyCode" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:PricingCurrencyCode" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:PaymentCurrencyCode" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:PaymentAlternativeCurrencyCode"
                      minOccurs="0"
                      maxOccurs="1"/>
         <xsd:element ref="cbc:AccountingCostCode" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:AccountingCost" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:LineCountNumeric" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cbc:BuyerReference" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cac:InvoicePeriod" minOccurs="0" maxOccurs="unbounded"/>
         <xsd:element ref="cac:OrderReference" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cac:BillingReference" minOccurs="0" maxOccurs="unbounded"/>
         <xsd:element ref="cac:DespatchDocumentReference"
                      minOccurs="0"
                      maxOccurs="unbounded"/>
         <xsd:element ref="cac:ReceiptDocumentReference"
                      minOccurs="0"
                      maxOccurs="unbounded"/>
         <xsd:element ref="cac:StatementDocumentReference"
                      minOccurs="0"
                      maxOccurs="unbounded"/>
         <xsd:element ref="cac:OriginatorDocumentReference"
                      minOccurs="0"
                      maxOccurs="unbounded"/>
         <xsd:element ref="cac:ContractDocumentReference"
                      minOccurs="0"
                      maxOccurs="unbounded"/>
         <xsd:element ref="cac:AdditionalDocumentReference"
                      minOccurs="0"
                      maxOccurs="unbounded"/>
         <xsd:element ref="cac:ProjectReference" minOccurs="0" maxOccurs="unbounded"/>
         <xsd:element ref="cac:Signature" minOccurs="0" maxOccurs="unbounded"/>
         <xsd:element ref="cac:AccountingSupplierParty" minOccurs="1" maxOccurs="1"/>
         <xsd:element ref="cac:AccountingCustomerParty" minOccurs="1" maxOccurs="1"/>
         <xsd:element ref="cac:PayeeParty" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cac:BuyerCustomerParty" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cac:SellerSupplierParty" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cac:TaxRepresentativeParty" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cac:Delivery" minOccurs="0" maxOccurs="unbounded"/>
         <xsd:element ref="cac:DeliveryTerms" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cac:PaymentMeans" minOccurs="0" maxOccurs="unbounded"/>
         <xsd:element ref="cac:PaymentTerms" minOccurs="0" maxOccurs="unbounded"/>
         <xsd:element ref="cac:PrepaidPayment" minOccurs="0" maxOccurs="unbounded"/>
         <xsd:element ref="cac:AllowanceCharge" minOccurs="0" maxOccurs="unbounded"/>
         <xsd:element ref="cac:TaxExchangeRate" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cac:PricingExchangeRate" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cac:PaymentExchangeRate" minOccurs="0" maxOccurs="1"/>
         <xsd:element ref="cac:PaymentAlternativeExchangeRate"
                      minOccurs="0"
                      maxOccurs="1"/>
         <xsd:element ref="cac:TaxTotal" minOccurs="0" maxOccurs="unbounded"/>
         <xsd:element ref="cac:WithholdingTaxTotal" minOccurs="0" maxOccurs="unbounded"/>
         <xsd:element ref="cac:LegalMonetaryTotal" minOccurs="1" maxOccurs="1"/>
         <xsd:element ref="cac:InvoiceLine" minOccurs="1" maxOccurs="unbounded"/>
      </xsd:sequence>
   </xsd:complexType>
</xsd:schema>

and the error message that shows me is

  

Error: Element not declared   'urn: oasis: names: specification: ubl: schema: xsd: CommonExtensionComponents-2:   ' Line: 30 Position: 11

I'm using XSD2CODE ++