SunCertPathBuilderException: unable to find valid certification path to requested target

[christopher pax]

im am trying to get my cas to work with shibboleth and i get this error:
sun.security.provider.certpath.SunCertPathBuilderException: unable to
find valid certification path to requested target

this is how i set up my credentials in my idp.xml file
<Credentials xmlns="urn:mace:shibboleth:credentials:1.0">
               <FileResolver Id="testshib_creds">
                       <Key>

<Path>file:///opt/shibboleth-idp/etc/testshib.key</Path>
                       </Key>
                       <Certificate>

<Path>file:///opt/shibboleth-idp/etc/testshib.crt</Path>
                       </Certificate>
               </FileResolver>

</Credentials>