OSB Validate action failed validation

The Exception logged is quite useless. You must examine the $fault in an error handler, to determine what went wrong:

<con:fault xmlns:con="http://www.bea.com/wli/sb/context">
  <con:errorCode>BEA-382505</con:errorCode>
  <con:reason>OSB Validate action failed validation</con:reason>
  <con:details>
    <con1:ValidationFailureDetail xmlns:con1="http://www.bea.com/wli/sb/stages/transform/config">
      <con1:message>string length (4) is greater than maxLength facet (3) for UOMType in namespace http://acme.pippo.com/po</con1:message>
      <con1:xmlLocation>
        <po:UOM xmlns:po="http://acme.pippo.com/po">PAL</po:UOM>
      </con1:xmlLocation>
      <con1:message>string length (4) is greater than maxLength facet (3) for UOMType in namespace http://acme.pippo.com/po</con1:message>
      <con1:xmlLocation>
        <po:UOM xmlns:po="http://acme.pippo.com/po">PAL</po:UOM>
      </con1:xmlLocation>
    </con1:ValidationFailureDetail>
  </con:details>
  <con:location>
    <con:node>PPL_acme_PO_FFMW_FilePoller_file</con:node>
    <con:pipeline>PPL_acme_PO_FFMW_FilePoller_file_request</con:pipeline>
    <con:stage>Validation</con:stage>
    <con:path>request-pipeline</con:path>
  </con:location>
</con:fault>

For some funny reason, the error message and location are repeated twice.