Have KIE Drools Workbench 6.2.0 Final installed inside a JBoss 7 Application Server local instance and Kie Server 6.2.0 Final inside a local Tomcat 7 instance.
What content type are you using in your POST request header?
As far as I remember, that error message happened if you didn't provide a content-type: application/xml in your request's header.