Need help with Unique Particle Attribution Rule

Hi,

I'm trying to parse an xsd with Xerces and I'm running into UPA rule
violation problems. Attached below is relevant sections in the xsd where
the problem is encountered. I'm finding it difficult to define the
'systemProvider' element in such way it doesn't violate this rule. Could
someone please assist me on how it can be done? 

(I tried to follow the name, first-name, last-name example to fix the
problem, but this particular element definition seems to be a bit more
complicated. Any help would be much appreciated.)

<xsd:element name="systemProvider">
    <xsd:complexType>
        <xsd:sequence>
            <xsd:sequence minOccurs="0" maxOccurs="unbounded">
                <xsd:element ref="admin"/>
                <xsd:element ref="error" minOccurs="0"/>
            </xsd:sequence>
            <xsd:element ref="deviceTypeInfo" minOccurs="0"
maxOccurs="unbounded"/>
            <xsd:element ref="error" minOccurs="0"/>
        </xsd:sequence>
    </xsd:complexType>
</xsd:element>

<!-- The following elements are referenced in the above piece of code
-->

<xsd:element name="deviceTypeInfo">
  <xsd:complexType>
   <xsd:sequence>
    <xsd:element ref="deviceType"/>
    <xsd:element ref="category"/>
    <xsd:element ref="maxPorts"/>
    <xsd:element ref="protocolSupported" maxOccurs="unbounded"/>
   </xsd:sequence>
  </xsd:complexType>
 </xsd:element>
 
<xsd:element name="protocolSupported">
  <xsd:complexType>
   <xsd:simpleContent>
    <xsd:extension base="xsd:string">
     <xsd:attribute name="default" use="optional">
      <xsd:simpleType>
       <xsd:restriction base="xsd:string">
        <xsd:enumeration value="true"/>
       </xsd:restriction>
      </xsd:simpleType>
     </xsd:attribute>
    </xsd:extension>
   </xsd:simpleContent>
  </xsd:complexType>
 </xsd:element>
 
<xsd:element name="error">
  <xsd:complexType>
   <xsd:sequence>
    <xsd:element ref="id"/>
    <xsd:element ref="summary"/>
    <xsd:element ref="detail" minOccurs="0"/>
   </xsd:sequence>
  </xsd:complexType>
 </xsd:element>
<xsd:element name="admin">
  <xsd:complexType>
   <xsd:sequence>
    <xsd:element ref="userId"/>
    <xsd:element ref="password" minOccurs="0"/>
    <xsd:element ref="userName" minOccurs="0"/>
   </xsd:sequence>
  </xsd:complexType>
 </xsd:element>

<xsd:element name="summary" type="xsd:string"/>
<xsd:element name="id" type="xsd:string"/>
<xsd:element name="detail" type="xsd:string"/>
<xsd:element name="userId" type="xsd:string"/>
<xsd:element name="password" type="xsd:string"/>
<xsd:element name="userName" type="xsd:string"/>
<xsd:element name="deviceType" type="xsd:string"/>
<xsd:element name="category" type="xsd:string"/>
<xsd:element name="maxPorts" type="xsd:string"/>


Thank you in advance.
Vino