Load xClass and xProperties, and link xProperties to multiple xClasses from AML

My project evolved to this exact problem of creating the 'xClass_xPropertyDefinition' and 'xClass_xProperty_Flatten'. Itemtypes. However, I was able to figure out how to call 'in xTree Context' 

<AML>
  <Item type='xClassificationTree' id="DFCA73A38AB9457F94EB6CA43CE617C7" action='edit'>
      <Relationships>
        <Item type='xClass_xPropertyDefinition' action="add">
          <source_id>C90E6B9D8A3045EAA21954F1B2FAD9C9</source_id>
          <related_id>6A0B41B77836433783A537A01FEA4BF8</related_id>
        </Item>
      </Relationships>
  </Item>
</AML>

The remaining problem is a permissions issue. I have added 'Can add' and 'update' permissions to the xClassificationTree, xClass, xPropertyDefinition, xClass_xPropertyDefinition, but this is the response I'm getting: 

<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">
  <SOAP-ENV:Body>
    <SOAP-ENV:Fault xmlns:af="http://www.aras.com/InnovatorFault">
      <faultcode>SOAP-ENV:Server.InsufficientPermissionsException</faultcode>
      <faultstring><![CDATA[You have insufficient permissions to perform 'add' operation.]]></faultstring>
      <detail>
        <af:legacy_detail><![CDATA[You have insufficient permissions to perform 'add' operation.]]></af:legacy_detail>
        <af:exception message="You have insufficient permissions to perform 'add' operation." type="Aras.Server.Core.InsufficientPermissionsException" />
        <af:permission type="can_add" itemtype="xClass_xPropertyDefinition" />
      </detail>
    </SOAP-ENV:Fault>
  </SOAP-ENV:Body>
</SOAP-ENV:Envelope>

If anyone has any ideas how to get around this, it would be greatly appreciated, I've been stuck on it for almost 2 weeks now...