As the jcr*.jar has been removed from SOA-P 5.1.0 as a result of SOA-2206, we should also remove the JCR Node mapping from jbpm.varmapping.xml:

<!-- JSR 170 JCR Node -->
<jbpm-type>
<matcher>
<bean class="org.jbpm.context.exe.matcher.JcrNodeMatcher" />
</matcher>
<variable-instance class="org.jbpm.context.exe.variableinstance.JcrNodeInstance" />
</jbpm-type>

Otherwise, an attempt to persist a jBPM variable which is not handled by any of the other matchers (eg. a non-serializable POJO), results in failure.

See SOA-3261 for more info.