XML validation error: expecting a tag that already exists

Question

I am developing an XML communication tool. My first step is to validate de xml I am receving. The communication is meant for V2G, so the xsd is on the web. I downloades the schemas an used a free web validator to check the message, but i get an error and i can not se the reason (i am new in xml).

the schema is as follows:

<!-- This XML document originates from the ISO/IEC 15118-2 standard which can be obtained from ISO at http://www.iso.org/iso/catalogue_detail.htm?csnumber=55366 -->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
    xmlns="urn:iso:15118:2:2010:AppProtocol"
    targetNamespace="urn:iso:15118:2:2010:AppProtocol">
    <xs:element name="supportedAppProtocolReq">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="AppProtocol" type="AppProtocolType" maxOccurs="20"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
    <xs:element name="supportedAppProtocolRes">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="ResponseCode" type="responseCodeType"/>
                <xs:element name="SchemaID" type="idType" minOccurs="0"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
    <xs:complexType name="AppProtocolType">
        <xs:sequence>
            <xs:element name="ProtocolNamespace" type="protocolNamespaceType"/>
            <xs:element name="VersionNumberMajor" type="xs:unsignedInt"/>
            <xs:element name="VersionNumberMinor" type="xs:unsignedInt"/>
            <xs:element name="SchemaID" type="idType"/>
            <xs:element name="Priority" type="priorityType"/>
        </xs:sequence>
    </xs:complexType>
    <xs:simpleType name="idType">
        <xs:restriction base="xs:unsignedByte"/>
    </xs:simpleType>
    <xs:simpleType name="protocolNameType">
        <xs:restriction base="xs:string">
            <xs:maxLength value="30"/>
        </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="protocolNamespaceType">
        <xs:restriction base="xs:anyURI">
            <xs:maxLength value="100"/>
        </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="priorityType">
        <xs:restriction base="xs:unsignedByte">
            <xs:minInclusive value="1"/>
            <xs:maxInclusive value="20"/>
        </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="responseCodeType">
        <xs:restriction base="xs:string">
            <xs:enumeration value="OK_SuccessfulNegotiation"/>
            <xs:enumeration value="OK_SuccessfulNegotiationWithMinorDeviation"/>
            <xs:enumeration value="Failed_NoNegotiation"/>
        </xs:restriction>
    </xs:simpleType>
</xs:schema>

And the messages is:

<?xml version="1.0" encoding="UTF-8"?>
<supportedAppProtocolReq xmlns="urn:iso:15118:2:2010:AppProtocol" xmlns:xsi="urn:iso:15118:2:2010:AppProtocol">
    <AppProtocol>
        <ProtocolNamespace>urn:din:70121:2012:MsgDef</ProtocolNamespace>
        <VersionNumberMajor>2</VersionNumberMajor>
        <VersionNumberMinor>1</VersionNumberMinor>
        <SchemaID>0</SchemaID>
        <Priority>1</Priority>
    </AppProtocol>
</supportedAppProtocolReq>

The error i get is:

Error - Line 3, 14: org.xml.sax.SAXParseException; lineNumber: 3; columnNumber: 14; cvc-complex-type.2.4.a: Invalid content was found starting with element 'AppProtocol'. One of '{AppProtocol}' is expected.

So, as I can understand, the invalid tag is the same tag that is asking for. Surely is a simple thing, but this is driving me nuts.