Unable to locate a reference

Hi,

I have obtain this error:
Unable to locate the reference to a supported schema type(DTD, W3W Schema) within this document instance. The error is in xsi:schemaLocation

<tp:CollaborationProtocolProfile
  xmlns:tp="http://www.oasis-open.org/committees/ebxml-cppa/schema/cpp-cpa-2_0.xsd"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:xlink="http://www.w3.org/1999/xlink"
  xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
  xmlns:xsd="http://www.w3.org/2001/XMLSchema"
  xsi:schemaLocation="cpp-cpa.xsd"
  tp:cppid="uri:Caibes-cpp" tp:version="2_0b">

what`s happend?? thanks very much